Mineral

A mineral is a naturally occurring, usually inorganic solid with a definite chemical composition and an ordered atomic arrangement, typically crystalline. The International Mineralogical Association (IMA) is the generally recognized standard body for the definition and nomenclature of mineral species, and as of August 2026 it recognizes 6,228 official species. Minerals are the basic building blocks of rocks, and their composition and structure are what geologists, chemists and engineers use to explain how the Earth's crust formed, changed and holds its resources. Silicates alone make up roughly 90% of the crust, so most of the planet's solid surface is mineral matter.

The subject is broad. It covers the criteria that separate a mineral from rocks, glass and biological materials; the atomic structures and chemical bonds that determine a mineral's properties; the classification schemes used to name and organize thousands of species; and the geological processes, from magma crystallization to hydrothermal activity, weathering and sedimentation, that create them. It also covers how minerals are identified and analyzed, how they are mined and processed, and why they matter for industry, energy systems, human health, cultural history and environmental management.

The entry proceeds from definition and structure, through physical and chemical properties and classification, to formation and occurrence, and then to identification, economic use, biological and cultural roles, historical development, and current questions about supply, environmental impact and extraterrestrial minerals.

Definition and Criteria for a Mineral

Geologists apply a working definition that requires several conditions to hold at once. To meet the definition of "mineral" used by most geologists, a substance must meet five requirements: it is naturally occurring, inorganic, solid, has a definite chemical composition, and has an ordered internal structure. The first condition excludes human-made materials. Steel is not a mineral because it is an alloy produced by people. The second excludes substances made by living organisms, so wood and pearls are made by organisms and thus are not minerals. The solid-state requirement excludes liquids and gases, although ice is classified as a mineral as long as it is naturally occurring.

The criterion of a natural origin has limits. Synthetic products, such as artificial diamonds, are therefore not minerals in the strict sense. Yet there is little difference between a synthetic and a natural gem, other than where they formed. Glass and other disordered solids fail the structural test. Glasses such as obsidian, which are disordered solids, liquids and gases do not have a crystalline structure and are therefore not minerals. Natural solids without a defined crystal structure, such as opal, are instead called mineraloids. Borderline cases include metamict phases, crystals whose lattice has been progressively destroyed by radiation from their own uranium or thorium; they are generally treated as no longer ordered enough to count as the original species.

Organic chemistry is treated more flexibly. An organic mineral is a scientifically recognized mineral that is made of an organic compound. These are so rare that they make up less than 0.1% of all known minerals. The IMA has officially recognized only a few dozen of these species. The clearest examples are compounds formed by geological processes acting on biological material: substances with such origins may be eligible if geological processes were involved in their genesis (as in the case of evenkite, derived from plant material; or taranakite, bat guano). By contrast, solid chemical substances that entirely form within living organisms, such as kidney stones or pearls, are not classified as minerals according to the IMA-CNMNC definition, since their formation does not involve any geological process. Hypothetical compounds predicted but never found in nature are also excluded.

A "mineral species" is an abstract category, while a specimen is a physical sample of it. All specimens of a given mineral, regardless of where, when, or how they were formed, have the same physical properties. This distinction was blurred in the nineteenth century, when many scientists named minerals that were only a different color or habit, or had a minor variation in chemistry. The development of X-ray crystallography in the 1930's and better chemical analyses has led to a clearer understanding of the difference between a mineral and variety of a mineral. The International Mineralogical Association took over responsibility for validating new species in 1959, and its Commission on New Minerals, Nomenclature and Classification (CNMNC) now administers the process.

Every new species is anchored to a type locality, the place where it was first found and described, and a type specimen, a sample kept as permanent reference. When a new mineral is described, the author should ensure that a type specimen is held as permanent reference material by at least one major museum or a nationally recognized mineral collection. Later revisions are judged against this material. If the original type specimen cannot be obtained, the investigator may propose a neotype to the CNMMN, clearly stating the efforts made to seek the original type-specimen, and providing satisfactory evidence for the identity of the neotype with the original.

Approval begins before publication. All proposals for introducing new minerals should be submitted to the CNMMN for approval before publication. The submission must supply data such as chemical formula (ideal formula), mineral symbol, type locality, crystal system, space group, structure determined, yes or no, unit-cell parameters, strongest lines in the X-ray powder diffraction pattern, type specimen repository and specimen number. The vote is a supermajority: a proposed new mineral will be considered approved if more than half of the members of the CNMMN vote on the proposal, and if more than two-thirds of these members have voted 'yes'. Only after this approval does a name become officially recognized.

Crystal Structure, Symmetry and Polymorphism

The crystal lattice and symmetry

A mineral's atoms or ions are arranged in a repeating three-dimensional pattern. The smallest block that, repeated by translation, reproduces the whole pattern is the unit cell, which is defined by three edge lengths and three angles. Geometrically, only 14 distinct lattice types can fill three-dimensional space; these are the Bravais lattices, first enumerated by Auguste Bravais in 1850. Their symmetry elements group them into seven crystal systems: triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal and cubic. The system constrains which external faces a crystal can develop and which physical properties are equal in different directions. Halite belongs to the cubic system, while quartz and calcite are trigonal.

X-ray diffraction and the definition of a species

Before the twentieth century, crystal structure was inferred mainly from external form and measured interfacial angles. In 1912 Max von Laue showed that crystals diffract X-rays, and the following year William Henry Bragg and William Lawrence Bragg related the diffraction angle to the spacing of atomic planes:

Here $\lambda$ is the X-ray wavelength, $d$ the interplanar spacing and $\theta$ the diffraction angle. Measured intensities allow the positions of atoms, their bond distances and their coordination to be determined, a process described in X-ray diffraction practice. Because a single composition can crystallize in different arrangements with very different properties, structure is treated as part of a species' identity. Two minerals with the same formula may therefore be distinct species, and a structure determination is often required before a name can be applied.

Polymorphism

Polymorphism occurs when one chemical composition adopts more than one crystal structure under different conditions. Silica (SiO2) provides a clear case. Quartz is the stable form at near-surface conditions, with silicon surrounded tetrahedrally by four oxygens. Stishovite, a tetragonal polymorph, has silicon in six-fold octahedral coordination, which raises its density from about 2.65 to about 4.3 g/cm³. It forms only at pressures of roughly 8 to 10 GPa, such as those generated by meteorite impacts or found in the deep mantle. Stishovite was identified in 1961 in material from Meteor Crater, Arizona, and its discovery helped establish the pressure-dependent silica sequence.

Carbon provides the opposite contrast in bonding. In diamond each carbon atom is covalently bonded to four neighbours in a rigid three-dimensional network, giving a density near 3.5 g/cm³. In graphite carbon forms planar hexagonal layers held together by weak forces, so the layers slide and the density is about 2.2 g/cm³. Graphite is the thermodynamically stable form at surface pressure and temperature, and diamond is metastable there; diamond crystallizes at depths of roughly 150 km or more, where the conversion is kinetically too slow to occur at the surface. Metamorphic minerals such as the Al2SiO5 polymorphs kyanite, andalusite and sillimanite are also used to infer the pressure and temperature of formation.

Polytypism

Polytypism is a special case in which layers of identical structure are stacked in different sequences along one axis. Polytypes share the same composition and the same layer, differing only in stacking, so they can be distinguished only by their symmetry and periodicity. Silicon carbide is the classic example, with more than 200 known polytypes, including the cubic 3C form and the hexagonal 4H and 6H forms. Zinc sulfide shows a similar pair: sphalerite is cubic, while wurtzite is hexagonal. Polytype names combine the number of layers in the repeat with a letter for the lattice type, which is one reason micas and carbides show such varied notation.

Pseudomorphs

A pseudomorph is a mineral that has the external crystal form of another mineral. Paramorphs retain the same composition but change structure, as in calcite that has replaced aragonite while keeping the aragonite shape. In epimorphs, a new mineral substitutes for the original one, as in limonite replacing pyrite and preserving the cubic outline of the pyrite crystal. Quartz pseudomorphs after fluorite are a further example. Because the outer shape can persist after the interior has been completely changed, a hand specimen may suggest a mineral that is absent from the crystal's inside. Identifying the original phase therefore requires internal analysis, such as X-ray diffraction or optical study of thin sections.

Chemical Composition and Bonding

A mineral's chemical composition is one of the attributes that define it, and the way its atoms are bonded largely determines its physical behaviour. 8 to 10 elements account for most of Earth's mass, but the elements are distributed unevenly. Each element's position in the periodic table predicts how readily it forms ions, and elements with similar chemical behaviour can often replace one another inside a crystal.

Ionic, covalent and metallic bonding

Three principal bonding styles build mineral structures. In ionic bonding, an atom transfers electrons to a neighbour, producing oppositely charged ions that attract electrostatically; halite is the standard example, in which sodium gives an electron to chlorine. In covalent bonding, neighbouring atoms share electron pairs, and the bonds are directional, so they constrain how atoms can be arranged. In metallic bonding, valence electrons are not tied to any one atom but move through the whole structure, which is why native gold, silver and copper fall into this category.

Few minerals sit at one extreme. Bonding in most minerals is neither 100% ionic, 100% covalent, nor 100% metallic; quartz is a common case where the silicon–oxygen bonds carry roughly equal ionic and covalent character. Halite and fluorite are near the ionic end because alkali metals readily lose electrons and halogens readily gain them.

How bond type controls properties

Bond strength broadly follows the order covalent, then ionic, then metallic. Covalent minerals are hard and tenacious, while metallic ones are usually not, and ionic minerals fall between. Melting temperatures show a similar pattern, while water solubility is highest for ionic crystals, whose bonds are weak enough to dissociate readily. A comparison of periclase (MgO) and halite (NaCl) illustrates the point: although the two share a similar crystal structure, periclase melts near 2,800 °C whereas halite melts at 801 °C, a difference attributed to the strength of their bonds. Bond type also influences symmetry. Ionic and metallic bonds are nondirectional, so they tend to yield highly symmetric structures, whereas covalent bonds are linear and produce lower-symmetry arrangements. Tighter packing of ions further raises hardness. Metallic bonding additionally allows electrical and thermal conduction, because the delocalised electrons carry charge and heat through the crystal.

Fixed stoichiometry and solid solutions

Some minerals have a nearly invariant formula; quartz (SiO₂) is an example. Many others vary in composition. Olivine, written (Mg,Fe)₂SiO₄, is a series in which iron and magnesium atoms can be substituted for each other without significantly changing the crystal structure. Because the two ions differ in size by only about 7%, complete solid solution between these two elements is observed in olivine. Plagioclase feldspar forms an even more classic continuous series: between the two end-members there is a continuous solid solution series, running from albite to anorthite. In this series, sodium and silicon substitute for calcium and aluminium in a coupled manner that keeps the overall charge balanced. Solid solutions are classified by how atoms enter the lattice. Substitutional solutions replace one atom with another, interstitial solutions place atoms into spaces between others (as carbon does in iron to make steel), and omission solutions leave vacancies, as in wüstite. Not all solutions are complete; some show only limited miscibility, which can be read from phase diagrams relating composition to temperature.

Isomorphism and substitution

Isomorphism refers to the substitution of similar ions without a change in structure type. A widely used rule of thumb holds that ions are typically interchangeable within a structure if their size does not differ by more than about 15% and valences do not differ by more than one unit. Iron(II) and magnesium meet both conditions, since both are divalent cations (both have a charge of +2), and this similarity is why they mix so freely in olivine. Calcium, with its larger ionic radius, enters the olivine structure only rarely. Charge balance is a constraint on substitution: the substitution of a cation of lower valence for another of similar size imparts a net negative charge to the structure, so the crystal must compensate, for example by coupling a second substitution elsewhere. Substitution of this kind also produces the temperature dependence seen in feldspars, where the higher the temperature of formation the more likely the feldspar is to be calcium-rich.

Trace elements and colour

Trace elements, present in amounts too small to alter a mineral's basic formula, can produce striking differences in appearance. In its purest form, the mineral corundum is colorless. Trace elements that become part of the mineral's crystal structure cause variations in its color. Chromium is the best-known colouring agent in corundum, and the more chromium, the stronger the red color. The mechanism is substitution: when chromium atoms substitute for a small percentage of the aluminum atoms in corundum's crystal structure, they absorb specific wavelengths of light and reflect back red. Iron and titanium together produce the blue of sapphire, showing that the same host structure can carry different colours depending on which minor constituents it incorporates.

Beyond colour, trace and minor constituents are used to infer how and where a mineral formed. The partitioning of elements such as nickel and chromium between olivine, pyroxene and melt, or the presence of europium anomalies in feldspar, records information about temperature, oxygen fugacity and melt composition. Such interpretations depend on the element's ionic size and charge, which control whether it can enter a particular site at all.

Physical Properties and Field Identification

Hardness, cleavage and fracture

Hardness is usually reported on the Mohs scale, which the Austrian mineralogist Friedrich Mohs devised in 1822 by ranking ten reference minerals according to which could scratch which. Mohs gave the softest mineral a value of 1 and the hardest a value of 10, and each mineral on the scale scratches the one below it but not the one above. The scale is ordinal rather than linear. The step from corundum (9) to diamond (10) represents a far larger difference in absolute scratch resistance than the step from talc (1) to gypsum (2). Hardness is set by the internal arrangement of atoms. Mohs hardness values are determined by the strength of a mineral's atomic bonds. Diamond, in which carbon atoms form a rigid three-dimensional network of covalent bonds, sits at the top of the scale, while graphite, whose layers are held together by much weaker forces, scores only 1–2.

Cleavage and fracture describe how a mineral breaks. Cleavage is the tendency of a mineral to split along certain planes. Because the planes are controlled by the lattice, cleavage surfaces are flat and reproducible: a mineral such as halite breaks into cubes, and the faces of a broken crystal are not restored once it fractures. Fracture describes the shape a mineral takes when broken and is typical of minerals without cleavage, such as quartz, which shows conchoidal (concave breakage reminiscent of glass), splintery, or uneven surfaces. Cleavage and fracture are distinct from hardness, but both reflect the same underlying bonding.

Luster, color, streak and specific gravity

Luster describes how light reflects from a fresh surface, commonly as metallic or nonmetallic (vitreous, pearly, silky and so on). Color is the most obvious property but the least dependable. Color is generally much less reliable than other properties, because trace impurities and surface weathering can change the appearance of the same mineral.

Streak, the color of a mineral's powder, is more stable. The test is usually performed on an unglazed porcelain plate with a hardness of about 7, and minerals harder than this will not leave a streak, but their powdered colors can be studied by crushing a small piece. Streak can separate look-alikes: pyrite, which has a brassy yellow color, leaves a greenish-black streak, while true gold leaves a yellow streak. Specular hematite, which looks silvery, has a red-brown streak. Streak color is not always what one might predict from examining the mineral.

Specific gravity is the ratio of a mineral's density to that of water. It expresses density as a ratio, comparing the mineral's density to the density of water at 1.0 g/cm³. Most minerals fall in the 2.5–3.5 range. Metal-rich minerals are much heavier, for example galena at about 7.5, while halite and gypsum are much less than this.

Crystal habit and form

Habit is the characteristic overall shape a mineral takes, such as cubic, prismatic, bladed, acicular (needle-like), fibrous or granular. Form refers to the crystal faces that share the same symmetry. Habit is controlled by the internal structure combined with the conditions of growth: the degree of supersaturation of the parent fluid or melt, temperature, the rate at which the crystal grows, the available space and the presence of impurities that bind to particular faces. Rapid growth in open space tends to produce well-formed crystals, while crowded or fast growth yields crusts, masses and aggregates. Because one species can show several habits, habit is a useful clue rather than a decisive identifier.

Simple field tests

Field identification usually proceeds from cheap, non-destructive tests toward more definitive ones. Hardness can be bracketed with everyday objects: a fingernail scratches minerals of about 2.5 and below, a copper coin scratches minerals of about 3, and a steel nail or window glass (about 5.5) marks the upper limit of many common minerals. If your mineral scratches glass, it's harder than 5.5. The scratch test should be run in both directions, so that the mineral and the reference object are each tested against the other.

The acid test is the standard field check for carbonates. Dilute hydrochloric acid, typically around 10%, is dropped onto a fresh surface. If the acid drop effervesces or fizzes on the surface, the specimen is calcite. Dolomite reacts much more slowly, so if dolomite is suspected, the specimen can be scratched to make a small amount of powder, and if the acid then fizzes slowly on the powder, the specimen is dolomite. The reaction releases carbon-dioxide gas. Household vinegar also works but gives a weaker effect, because acetic acid is a weaker acid. Acid should be handled with gloves and eye protection.

Magnetism is equally quick. Magnetite is the only common mineral that is strongly attracted to a simple handheld magnet. Some other iron-bearing minerals are only weakly magnetic; ilmenite and some types of hematite are weakly magnetic.

Because a single test rarely settles an identity, field results are treated as a screen. Often a single series of tests may not key the user in to the correct identification. Confirmation through microscopy, X-ray diffraction or chemical analysis follows in the laboratory.

Optical, Electrical and Magnetic Properties

Most of the physical behaviour that mineralogists use for identification follows from the way a crystal's internal arrangement interacts with light, electric fields and magnetic fields. In an optically isotropic mineral, such as garnet or halite in the cubic system, light travels at the same speed in every direction and is described by a single refractive index. In anisotropic minerals, which include most crystals outside the cubic system, the refractive index depends on direction. The difference between the largest and smallest refractive indices is the birefringence, also called double refraction. When light enters such a crystal, it splits into two rays that travel at different speeds. After they recombine through a second polarizer set at right angles, they produce interference colours. Because birefringence is a fixed property of each mineral, the colours seen at a known thickness can be matched to standard charts to estimate its value.

In polarized-light microscopy, geologists examine rock slices about 30 micrometres thick, known as thin sections. A petrographic microscope has two polarizers and a rotating stage. Under plane-polarized light, pleochroism appears when a mineral changes colour as the stage turns, because it absorbs light differently along different crystallographic directions. Biotite, a common mica, is a standard example, and tourmaline shows a similar effect. Under crossed polarizers, the same grain may show interference colours, extinction when it goes dark at specific rotations, and twinning patterns. Together with refractive index, relief, cleavage and crystal habit, these observations allow many rock-forming minerals to be identified within a single slide, and they also reveal how a rock was deformed or altered.

Some minerals generate electric charge when their structure is mechanically or thermally disturbed, which is the basis of piezoelectricity and pyroelectricity. The Curie brothers, Jacques and Pierre, demonstrated piezoelectricity in 1880 and 1881 in crystals including quartz and tourmaline, and Gabriel Lippmann deduced the converse effect in 1881, in which an applied voltage changes a crystal's shape. In quartz, the effect arises from the displacement of silicon and oxygen ions within the silica framework when the crystal is compressed or stretched. Quartz is piezoelectric but, because its symmetry is not polar, it is not generally considered pyroelectric. Tourmaline is both: its structure has a polar axis, so heating or cooling it produces charge at opposite ends. This was long known from observations dating back to antiquity, but the mechanism was not explained until the nineteenth century. Piezoelectric quartz, once mined in natural form, is now largely grown synthetically under hydrothermal conditions and is used as a frequency-control element in clocks, radio circuits and filters. Semiconductivity is a separate property, in which conductivity depends on band structure and impurities rather than on any polar axis. Sulfide minerals such as galena and pyrite have been used as semiconductors in early radio detectors, and modern electronics depend on semiconductor materials such as silicon, which is an element rather than a mineral and is produced largely from quartz.

Magnetic behaviour depends on the arrangement of electron spins in iron-bearing minerals. Magnetite, a spinel-type iron oxide, is ferrimagnetic, and it loses its spontaneous magnetization above its Curie temperature of about 580 °C. Hematite, the other common natural iron oxide, has a higher Curie point of about 675–680 °C. When a rock cools through these temperatures in Earth's magnetic field, the magnetic moments of its grains align with the field and become locked into position. This thermal remanent magnetization is highly stable and can survive for very long periods, making it the basis of paleomagnetism. Geologists use it to reconstruct the direction and intensity of the ancient field, to track the motion of continents and to document reversals of Earth's magnetic polarity. Because a partial reheating can reset or partly overprint the signal, paleomagnetic work often uses stepwise demagnetization, in which a sample is heated in steps and its remaining magnetization is measured after each one.

Minerals containing uranium, thorium or potassium are radioactive and contain a built-in clock. Uranium-238 decays to lead-206 with a half-life of about 4.47 billion years, and uranium-235 decays to lead-207 with a half-life of about 0.70 billion years. Zircon is the most widely used mineral for this purpose, because it incorporates uranium readily but excludes lead when it crystallizes, and it resists diffusion of lead at high temperatures. Analysts measure the ratios of parent and daughter isotopes and check the results against each other, which allows the age to be cross-validated. Some zircons from Western Australia's Jack Hills have yielded ages of about 4.4 billion years, among the oldest dated materials on Earth. Radiation damage over time can make a zircon grain amorphous, a condition called metamictization, which can disturb isotope systems and must be considered when interpreting results. Potassium-argon and argon-argon methods use micas and feldspars for similar purposes. The concept of closure temperature, the point below which a mineral retains its daughter isotopes, is central to these methods. Lead diffusion in magnetite, for example, is slow enough that closure temperatures above 500 °C are plausible in some geological settings.

Classification Systems

From descriptive schemes to structure-based systems

Early mineral classification was practical. Miners and early geologists sorted specimens by their dominant element, such as iron or copper, and by visible properties such as color and hardness. The first systematic scheme is usually credited to James Dwight Dana, whose System of Mineralogy appeared in 1837. Dana arranged minerals first by chemistry and then by atomic structure or symmetry, and the fourth edition of 1854 is often cited as the point at which the system was firmly based on chemical composition. Dana's scheme was revised over later editions and was extended in 1997 to reflect the growing body of structural data.

The decisive shift came in the twentieth century. Once X-ray crystallography showed that two minerals with the same formula could have different internal arrangements, composition alone was no longer enough to define a species. Pioneers of the method, notably William Henry Bragg and Victor Goldschmidt, used structural evidence to group silicates by their atomic architecture. Karl Hugo Strunz then built a chemical-structural scheme in his Mineralogische Tabellen (1941), which combined crystallographic criteria with chemical composition and superseded the older Dana tables for many purposes. Later editions were co-written with Ernest Nickel, which is why the scheme is also called the Nickel–Strunz classification.

The Dana and Strunz systems

The Dana system uses a numerical code of four groups separated by dots. The first number gives the class, the second the type (sometimes reflecting atomic structure), the third a group of minerals with similar structure, and the fourth the individual species. Because each mineral receives a unique code, the system resolves confusion caused by synonyms. It remains widely used in English-speaking countries, particularly the United States, and in academic and historical contexts, though it is considered relatively rigid.

The Strunz system is more flexible. Its primary division is by chemical class, and each class is then divided by structural criteria. Within a class, subdivisions depend on the polymerization of anion polyhedra, the cation-to-anion ratio, and the presence or absence of hydroxyl groups or water. In the silicates, for example, the degree of linkage between silicon-oxygen units decides much of the grouping. The Strunz code for a mineral combines a class number, division and family letters, and a group number, so one code can place a mineral in a structural family as well as a chemical one.

IMA-CNMNC hierarchy and the "Strunz 10" version

The Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA) has proposed a formal nesting of levels: class, subclass, family, supergroup, group and subgroup (or series). The proposal by Mills and colleagues in 2009 defines a mineral group as two or more minerals sharing essentially the same structure and composed of chemically similar elements. At the top level, species are sorted by the main anion, by an anionic complex such as sulfate or carbonate, or by the absence of an anion, which is the case for native elements. Unoccupied structural sites are treated like chemical elements when placing a group.

The version of the Strunz scheme that the IMA and many mineralogical databases now use is often called "Strunz 10." It divides all minerals into ten classes according to the chemical identity of their principal anion, with each class labelled by a two-digit number. The main change from the ninth edition (2001) is that borates, previously grouped with carbonates and nitrates, form a class of their own. The ten-class version was developed but not formally published as a book, so it is referenced mainly through the IMA list and online databases.

Major classes in practice

The ten classes are native elements; sulfides and sulfosalts; halides; oxides and hydroxides; carbonates and nitrates; borates; sulfates; phosphates, arsenates and vanadates; silicates; and organic compounds. Native elements contain a single element, such as gold, copper, sulfur or graphite. Sulfides and sulfosalts, which include many of the world's principal metal ores, are dominated by sulfur-bearing anions and tend to be dense and opaque. Halides such as halite and fluorite have halogen anions, while oxides and hydroxides cover a wide range of ore and industrial minerals. Carbonates are typified by calcite and dolomite, and sulfates by gypsum and barite. Phosphates, arsenates and vanadates share tetrahedral oxyanions, and organic minerals, a small and recently expanded class, contain carbon-based anions.

Silicates are by far the largest class and include most of the rock-forming minerals, such as feldspars, micas and pyroxenes. Their classification depends heavily on how silicon-oxygen tetrahedra share corners, which is why silicates are subdivided by structure rather than by chemistry alone. Because the classes are defined by anions, a single cation-rich species can appear in different classes depending on its anion chemistry, and unusual species sometimes require special handling under the rules for groups and series.

Silicate Minerals and Rock-Forming Minerals

Why silicates dominate

Silicates form the largest mineral class by a wide margin. One common estimate puts them at roughly 95 percent of the crust and uppermost mantle. Their abundance follows from geochemistry: oxygen and silicon are the two most plentiful elements in the crust, and they combine readily. The basic unit is a silicon cation (Si⁴⁺) at the centre of four oxygen anions (O²⁻) placed at the corners of a regular tetrahedron, giving the group $(\mathrm{SiO_4})^{4-}$. The Si–O bond is roughly half ionic and half covalent, which makes it strong.

Each oxygen contributes only half of its bonding capacity to a given silicon, so the remaining capacity can attach to a second silicon. Tetrahedra therefore link by sharing corner oxygens, a process called polymerization. The number of shared corners, from one to four, sets the structural class:

• Nesosilicates (isolated tetrahedra), such as olivine and garnet.
• Sorosilicates, in which pairs of tetrahedra share one oxygen to form $\mathrm{Si_2O_7}$ groups.
• Cyclosilicates (rings), such as the sixfold $\mathrm{Si_6O_{18}}$ ring type.
• Inosilicates (chains). Single chains, typified by pyroxenes, have a silicon-to-oxygen ratio of 1:3. Double chains, typified by amphiboles, are wider and more complex.
• Phyllosilicates (sheets), in which each tetrahedron shares three oxygens. Micas, clay minerals and serpentine belong here.
• Tectosilicates (frameworks), in which all four oxygens are shared. Quartz and the feldspars are the principal examples.

Cations such as Mg²⁺, Fe²⁺/Fe³⁺, Ca²⁺, Na⁺ and K⁺ sit in the interstices and balance the negative charge of the anionic framework. Because these cations can vary in identity and proportion, a single structural type yields many species.

Major rock-forming groups

The silicate groups that make up most igneous and metamorphic rocks show a clear pattern of structure and composition:

• Olivine ((Mg,Fe)₂SiO₄) is an isolated-tetrahedron mineral that dominates the upper mantle and ultramafic rocks, and it is a major constituent of basalt and gabbro.
• Pyroxenes, such as augite, are single-chain silicates found in basalt, gabbro and many mafic rocks.
• Amphiboles, such as hornblende, are double-chain silicates that characterize intermediate igneous rocks like diorite and andesite.
• Micas are sheet silicates. Biotite is common in granite and other felsic rocks, while muscovite is typical of felsic and metamorphic rocks.
• Feldspars are framework silicates and are generally regarded as the most abundant mineral group in the crust. Calcium-rich plagioclase occurs in mafic rocks, while sodium-rich plagioclase and potassium feldspar are typical of granite.
• Quartz is a framework of pure SiO₂. Its chemical and mechanical stability makes it abundant in granite, sandstone and many metamorphic rocks.

Assemblages as indicators of conditions

Mineral assemblages record the temperature, pressure and chemistry under which a rock formed. The clearest framework for igneous rocks is Bowen's reaction series, which the Canadian petrologist Norman L. Bowen developed in the early twentieth century from experiments on cooling melts. The discontinuous branch begins with olivine at the highest temperatures and then passes through pyroxene and amphibole to biotite, with each mineral reacting with the melt to form the next. The continuous branch shows calcium-rich plagioclase gradually changing composition toward sodium-rich plagioclase as the melt cools. At low temperatures the two branches converge on potassium feldspar, muscovite and quartz. The series explains why basalt is dominated by olivine, pyroxene and calcium-rich plagioclase while granite is rich in quartz, potassium feldspar and mica. Later work has refined the model to account for pressure, volatile content and partial melting.

In metamorphic rocks, assemblages are interpreted through phase relations: the stable combination of minerals at a given temperature and pressure, often displayed in phase diagrams. Changes in assemblage record reactions that proceed as rocks are heated or buried.

Non-silicate rock-forming minerals

Several non-silicates are abundant enough to be classed as rock-forming. Calcite (CaCO₃) and dolomite make up most limestone and marble. Calcite precipitates from seawater and is also produced by organisms that build shells and skeletons, and dolomite commonly forms by the partial replacement of calcite. Gypsum (CaSO₄·2H₂O) and halite (NaCl) precipitate as seawater or saline groundwater evaporates. They dominate evaporite sequences that accumulate in restricted marine basins, playas and closed lakes, often alongside anhydrite. Because these minerals form from solution rather than from silicate melts, their occurrence reflects climate, salinity and water chemistry rather than magmatic cooling history.

Formation Processes and Geological Occurrence

Crystallization from magma and lava

Minerals that grow from a cooling silicate melt tend to appear in a repeatable order. Norman L. Bowen melted powdered mafic rock, let the melt cool slowly to a set temperature, and then quenched it to record which phases had formed he melted powdered mafic igneous rock by raising its temperature to about 1280°C to make artificial magma. Then he let the melt slowly cool to a preset temperature and pressure. The resulting model, Bowen's reaction series, has two branches. On the discontinuous side, earlier-formed crystals react with the remaining liquid to produce the next phase, so olivine is transformed into pyroxene and then into amphibole early-formed crystals of olivine react with later liquids to form pyroxene crystals, and these, in turn, may further react with still later liquids to form amphiboles.. On the continuous side, plagioclase does not change type abruptly; its composition shifts from calcium-rich toward sodium-rich the evolution of the plagioclase feldspars as they evolve from being calcium-rich to more sodium-rich.. The last liquid yields potassium feldspar, muscovite and quartz Potassium Feldspar, Muscovite, and Quartz crystallize in that order, and comprise the Lower Series..

Because each growing crystal takes up certain elements in preference to others, the residual liquid changes composition as it cools Bowen noticed that as new crystal form, it preferentially extracts certain chemical from the melt. Hence, the chemical composition of the residual melt gradually changes as the melt cools.. This drift is one reason a single parent magma can produce a range of rock types from basalt to granite. Lava that reaches the surface cools far faster than intrusive bodies, so its crystals are often tiny or absent and glassy textures are common.

Pegmatites represent the coarse end of this sequence. They form from the final, volatile-rich fraction of a granitic melt. Dissolved water lowers both the melting temperature and the viscosity of the liquid water, as a dissolved constituent in magma, lowers its melting temperature significantly. Water also lowers the viscosity (resistance to flow) of the residual melt, which allows ions to reach growing crystal faces readily. Large grain size therefore reflects a water-rich chemistry rather than unusually slow cooling The extra large size does not mean that they cooled extra slowly. Instead, the large crystals of a pegmatite formed in a magma that was extra rich in dissolved water. The water allowed the necessary elements to diffuse extra fast to the sites of crystallization. Individual grains commonly reach several centimeters, and some reach meters The individual mineral grains in pegmatite are usually several centimeters across and may occasionally reach lengths of several meters. Pegmatite bodies often occupy veins that opened late in the solidification of a larger intrusion Pegmatites often form in veins that opened up at the end of the crystallization of a large intrusive mass.. The same residual fluids concentrate lithium, sodium, potassium, rubidium and cesium they will promote concentration of such elements as lithium, sodium, potassium, rubidium, and cesium in that melt., which is why many gem and rare-element minerals are found in pegmatites.

Hydrothermal processes

Hydrothermal deposits form when hot, water-based solutions move through rock and drop their dissolved load. As hydrothermal solutions migrate through the rock, they can deposit minerals by filling natural openings or reacting with the surrounding rock, creating various deposit types such as veins, cavity-filling deposits, and metasomatic replacement deposits. Faults and fissures serve as the main conduits Hydrothermal solutions find ready-made escape routes through the surrounding country rock in the form of faults and fissures.. Where minerals fill open space, veins result; where the fluid dissolves the host rock and new minerals take its place, replacement bodies result A hydrothermal replacement deposit occurs when hot circulating aqueous solutions replace the original rock with new mineral species.. Carbonate rocks are especially susceptible to this style of replacement This typically occurs in more soluble rocks such as limestone..

Typical ore minerals include native gold (Au) and the sulfides galena (PbS), sphalerite (ZnS), chalcopyrite (CuFeS_2), pyrite (FeS_2), bornite (Cu_5FeS_4), arsenopyrite (FeAsS), and tetrahedrite ((Cu,Ag)_12Sb_4S_13). Some systems are driven by seawater. On the seafloor near volcanic arcs, hot, metal-rich hydrothermal fluids mix with cold seawater and precipitate metal sulfides. Mississippi Valley-type deposits involve fluids that travel far from their source; MVT deposits are formed from hydrothermal fluids that have migrated for considerable distances (sometimes >100 km) from their source. They consist of veins and replacement bodies which have been precipitated from low-temperature, highly saline metalliferous brines expelled from deep sedimentary basins..

Metamorphic reactions

Metamorphism alters existing rock in the solid state. Rising temperature and pressure drive recrystallization of grains and the breakdown of unstable minerals into new assemblages, with fluids often accelerating the reactions. Pelitic rocks, for example, may develop garnet, staurolite, kyanite or sillimanite depending on the depth and heat of burial. Contact metamorphism around intrusions produces fine-grained hornfels, whereas regional metamorphism during mountain building affects large volumes of crust. Limestone recrystallizes to marble and sandstone to quartzite. Pentti Eskola's facies concept, introduced in 1915, grouped these assemblages by pressure and temperature. The process stops short of bulk melting; when partial melting begins at high grade, the rock enters the transition to magmatism.

Precipitation and evaporation

In closed or arid basins, evaporation concentrates dissolved salts until they crystallize. Minerals generally precipitate in order of increasing solubility: calcite first, then gypsum or anhydrite, then halite, and finally potassium and magnesium salts such as sylvite and carnallite. Thick evaporite sequences, such as the Permian Zechstein deposits of northern Europe, record repeated drying of marine basins. Some saline lakes, such as Lake Magadi in East Africa, precipitate carbonate minerals such as trona. In caves, water dripping from the ceiling loses carbon dioxide and deposits calcite as stalactites and stalagmites. Sedimentary cements, commonly calcite, silica or iron oxides, fill pore spaces between grains during burial and turn loose sand into sandstone.

Weathering, Stability and the Geochemical Cycle

Primary minerals crystallize in magmas and metamorphic rocks under conditions that often differ sharply from the surface. When rocks are uplifted and exposed, water, oxygen and dissolved carbon dioxide attack them. Chemical weathering is a process in which water and weak acids in groundwater react with granites and other rocks made of orthoclase feldspar, breaking and reforming their chemical bonds. Physical weathering, such as freeze-thaw cycles and salt crystal growth, meanwhile fractures rock and exposes fresh mineral surfaces to chemical attack, so the two processes usually work together. Erosion then carries the fragments and dissolved products away.

Feldspar is the main source of clay. During weathering, feldspar is altered by hydrolysis, forming clay minerals such as kaolinites and smectites. Kaolinite, Al₂Si₂O₅(OH)₄, has a simple layered structure in which each layer pairs one silica sheet with one alumina sheet. This simple stacking makes it relatively chemically inert and stable compared with many other clay minerals. The type of clay that forms depends on the setting. Warm, wet tropical climates favour kaolinite, while geothermal fluids rich in CO₂ produce tubular halloysite. Illite requires relatively alkaline water, and smectite typically forms from volcanic ash in dry environments. Secondary minerals may result from modification of the primary structure, or from precipitation of dissolved constituents into a more stable arrangement. Under strongly weathering conditions, iron and aluminium also precipitate as secondary oxides and hydroxides, which give tropical soils their red and yellow colours.

Whether a mineral persists depends on its stability field, and this is most clearly shown on a phase diagram. Such diagrams map the temperature, pressure and composition ranges in which each phase is thermodynamically stable. The stability fields of polymorphs such as kyanite, sillimanite and andalusite are the ranges of pressure and temperature where each one is stable. Surface weathering can be read the same way. Kaolinite is not stable at high temperature; rocks that contain kaolinite and quartz must have formed below about 300 °C. Diamond illustrates the metastable case. Thermodynamics predicts that diamonds should convert to graphite, yet many diamonds persist as metastable grains. Under surface conditions, most primary silicates are unstable, and the reaction toward clays and oxides proceeds as long as water and reactive solutes are present. The same thermodynamic logic also explains why a mineral that is stable at depth may weather at the surface.

Weathering is central to the carbon cycle over long timescales. A negative feedback links the rate of silicate weathering, surface temperature and the partial pressure of CO₂, and this regulates atmospheric CO₂ over periods longer than a million years. Studies find that CO₂ removal by continental silicate weathering depends strongly on temperature and only weakly on CO₂ pressure. The overall reaction of calcium silicate with CO₂ to form carbonate and silica is the key step in which atmospheric CO₂ is drawn down by precipitation of carbonate. The resulting carbonate burial balances the CO₂ supplied by volcanic outgassing at steady state. Carbonate weathering behaves differently: most of the CO₂ it consumes returns to the atmosphere when the carbonate reprecipitates, so its net effect on climate is smaller.

Weathering also releases the nutrients that support ecosystems. Apatite supplies phosphate, while feldspars, micas and other silicates release potassium, calcium, magnesium and iron as they break down. Rivers carry the dissolved products to the sea, where they support aquatic production. Soil fertility depends on how quickly these nutrients are released relative to how fast plants and leaching remove them. Very old, strongly weathered tropical soils often become phosphorus-limited because their primary phosphorus reserves have been largely depleted, a condition that links the geochemistry of minerals directly to ecosystem productivity and to the need for fertilizer in agriculture.

Biomineralization

Biomineralization is the process by which living organisms form minerals, either inside their cells or outside them. Examples include iron and gold deposits in bacteria and other unicellular organisms, silicates in algae and diatoms, carbonates in diatoms and nonvertebrates, and calcium phosphates and carbonates in vertebrates. Organisms belonging to all five kingdoms have been identified to precipitate minerals. What separates biological mineral formation from abiotic precipitation is the degree of control the organism exerts over nucleation, growth and location. Earth scientists long studied minerals that formed without life, and biomineralization became a central topic only as biogeochemistry matured.

Skeletons, Shells and Teeth

Calcium carbonate is the most widespread biomineral. Calcite and aragonite make up the shells of mollusks, the plates of coccolithophores and the skeletons of corals, and some of these shells carry nacreous layers in which mineral platelets alternate with organic sheets. Vertebrate bones and teeth are built from a calcium phosphate close to hydroxyapatite, which is combined with collagen and carbonate substitution. Diatoms and radiolarians instead construct skeletons from hydrated amorphous silica, producing the intricate frustules and lattice shells visible in marine sediments.

Organic molecules such as proteins and polysaccharides usually guide these structures. In most cases, biomineralization involves a combination of organic molecules, such as proteins or polysaccharides, and inorganic ions from the surrounding environment. Cell surfaces can serve as nucleation sites, so that the secondary precipitation of minerals occurs as a result of interactions between biological activity and the environment. This biological control allows organisms to produce crystals with unusual morphologies, structures and properties that are difficult to obtain in synthetic systems. Biominerals also carry chemical records of their surroundings. Biologically produced minerals often contain embedded within their compositions, signatures that reflect the external environment in which the animal lived. Geochemists therefore use shell chemistry to reconstruct past seawater temperatures and salinities.

Magnetotactic Bacteria and Magnetite

Magnetotactic bacteria are the clearest example of an organism that uses a mineral for navigation. They are aquatic microorganisms with the ability to biomineralise membrane-enclosed magnetic nanoparticles, called magnetosomes. These magnetosomes are arranged into a chain that behaves as a magnetic compass, allowing the bacteria to align in and navigate along the Earth's magnetic field lines. Most magnetosome crystals are magnetite, although some species make greigite. Mature crystals of both minerals generally lie within the single-magnetic-domain size range, about 35 to 120 nm, in which they have the highest possible magnetic moment per unit volume.

The crystals are formed under tight genetic control. The roughly 20 magnetosome-specific proteins have functions in vesicle formation, magnetosomal iron transport, and the control of crystallization and intracellular arrangement of magnetite particles. Within the vesicle, the Mms-proteins are a unique set of transmembrane or soluble proteins that control the nucleation and directed growth of magnetite or greigite within the magnetosome vesicles. The resulting crystals are unusually uniform, and the chain arrangement maximizes the cell's overall magnetic dipole. Whether magnetosomes serve only navigation is debated. The original magneto-aerotaxis hypothesis proposes that navigation helps cells find the oxygen gradients where they feed, while other proposals suggest roles in iron storage or in removing reactive oxygen species. It was recently shown that magnetite magnetosomes scavenge reactive oxygen species in Magnetospirillum gryphiswaldense and exhibit peroxidase-like activities.

Biomineralization in the Fossil Record

Biominerals dominate the preserved record of animal life because hard tissues survive burial far better than soft ones. Skeletons made of calcium carbonate or calcium phosphate are fundamentally more likely to enter the fossil record than non-mineralized tissues. This bias is especially strong in the early Cambrian. Latest Ediacaran and early Cambrian rocks also preserve a staggering diversity of animal skeletons, largely in the form of small shelly fossils. Many of these early skeletons were made of apatite, the same mineral as bone, while others were calcium carbonate, like modern bivalves or snails.

The timing of skeletal origins remains debated. Mineralized skeletons appeared in many animal groups within a relatively narrow interval, and some researchers argue that they arose through the co-option of a conserved genetic and organic toolkit rather than through independent invention each time. Evidence points towards multiple instances of the evolution of biomineralization through the co-option of an inherited organic skeleton and genetic toolkit. Other workers stress that the Cambrian pattern may partly reflect preservation. Soft-bodied faunas such as the Burgess Shale show that the vast majority of taxa and individuals were non-biomineralizing, which means the shelly record underrepresents much of the early animal diversity. Ocean chemistry is also invoked: the Cambrian radiation occurred mainly during a time of aragonite and high-magnesium calcite seas.

Ore Minerals and Economic Geology

Ore minerals, gangue and grade

Economic geology separates the minerals that a deposit is mined for from the rest of the rock. The valuable phases are the ore minerals, such as chalcopyrite for copper or galena for lead. The surrounding material is gangue. Quartz, calcite, feldspar and various silicates are typical examples of gangue. No deposit consists of pure ore; every one carries a share of valueless minerals. In hydrothermal veins, gangue minerals such as quartz, calcite and fluorite are common because they precipitate from hot, mineral-rich fluids moving through fractures in the crust.

Gangue is not always harmless. In iron ore, for example, pyrite and apatite introduce sulfur and phosphorus, which degrade steel unless they are removed. The amount of gangue also drives cost. When gangue is hard to separate, processing requires more advanced technology, energy and reagents, and if these costs exceed the revenue from the metal, the deposit becomes unprofitable and may be closed or abandoned.

Viability depends on several measurable quantities. Grade is the proportion of valuable material in the rock. It is reported as a weight percentage, or in grams per tonne for low-concentration ores. Tonnage, the total volume of ore, must also be large enough to repay the capital spent on a mine. Because a cut-off grade is set by prices and recovery rates, it is not fixed. When metal prices rise, lower-grade material becomes profitable, so the economically recoverable deposit effectively grows. Low-grade deposits can still be worked where they are very large and processed at scale, as with some open-pit copper and iron operations.

Major ore-forming minerals and their settings

• Copper: Most copper comes from porphyry deposits, which form around intrusions above subduction zones. The principal ore minerals are chalcopyrite and bornite, typically disseminated through large volumes of altered rock at low grades.
• Iron: Banded iron formations, mostly deposited in the Precambrian, supply the bulk of iron ore. Hematite and magnetite are the main ore minerals, with major reserves in Western Australia and Brazil.
• Lead and zinc: Galena and sphalerite occur in sedimentary-hosted Mississippi Valley-type deposits and in volcanogenic massive sulfide bodies on the seafloor.
• Aluminum: Bauxite forms by intense tropical weathering of aluminous rocks, leaving gibbsite, boehmite and diaspore concentrated in laterite profiles.
• Gold: Gold occurs in quartz veins, in orogenic lode systems and in placers formed when erosion releases grains into rivers.
• Rare earth elements: Bastnäsite and monazite are concentrated in carbonatites, and ion-adsorption clays in southern China and Southeast Asia host elements that are easily leached.

Industrial minerals

Industrial minerals are valued for their physical or chemical properties rather than for metal content. Limestone supplies cement, lime and flux for steelmaking. Gypsum is used for plaster and wallboard. Potash, which contains potassium salts such as sylvite, is mainly used in fertilizer. Kaolin, a clay dominated by kaolinite, is used in ceramics, paper coating and refractories. Because their markets depend on bulk quality, transport distance often limits their trade more than geology does.

Critical minerals and market concentration

The term critical minerals describes commodities whose supply is vulnerable to disruption and important to the economy or security. The United States Geological Survey's 2025 list contains 60 entries, half carried over from 2022, and it includes 15 rare earth elements. The list is updated at least every two years, reflecting changing supply conditions. The USGS also states that rare earths would impose the highest cost on the US economy if supply were disrupted.

Concentration is the central issue. The International Energy Agency reports that China is the leading refiner for 19 of 20 important strategic minerals, with an average market share of 70%. For rare earths used in magnets, China accounted for around 60% of global mining output in 2024, and its share of separation and refining is higher, at about 91% according to the same analysis. Other estimates of processing share are around 90%, so the exact figure depends on the base year and definition used.

Trade policy has amplified this concentration. Expanded Chinese controls introduced in October 2025 were suspended for one year, while earlier licensing requirements from April 2025 remain in force for seven medium and heavy rare earth elements. The suspension is due to expire on 10 November 2026. One analysis reports that foreign-made products containing 0.1 percent or more of Chinese-origin rare earths require a license. Demand growth in magnets for electric vehicles, wind turbines and defense systems, which rely on these elements, means that such policy decisions move prices and investment decisions across the market.

Mining, Extraction and Processing

Choosing a mining method

Depth and deposit shape are the main factors in choosing between surface and underground extraction. Open-pit mining utilizes terraced surface excavations to harvest shallow deposits, whereas underground mining employs complex tunnel networks for deep-seated orebodies. Surface hard-rock mines can work almost any ore configuration, but many underground methods were developed for specific deposit geometries and rock conditions in response to the requirements of differing geometry and geomechanical properties of the host and surrounding rock. Dip also matters: steeply dipping veins favor underground selectivity.

Pit depth raises costs, which is why many deposits switch methods at some point. Underground working becomes economically attractive when open-pit stripping ratios become too high. Slope stability and the cost of automating deep pits also weigh on the decision, and in some cases underground mining by caving methods may be less costly than open pit mining operating at greater depths. Transition depths calculated for individual deposits vary widely. One Chinese iron mine yielded a calculated transition of 388 m, while an Iranian iron deposit's optimal transition point was 315 m for scenario 1 and 360 m below the surface for scenarios 2 and 3, the latter allowing for production delays during the changeover.

From ore to concentrate

Ore rarely contains a metal-bearing mineral in a form that can be smelted directly, so beneficiation first separates the valuable grains from waste rock. Its first stage, comminution, combines crushing and grinding. Comminution reduces ROM ore to a particle size fine enough that individual mineral grains become physically separable from surrounding gangue. This critical threshold is known as the liberation size, and it varies by deposit and mineral type. Comminution is also energy-intensive; practitioners often aim for "more crushing and less grinding" to reduce grinding energy use. Concentration and separation use gravity, magnetic or flotation methods, and dewatering follows, using filters and thickeners.

Flotation relies on surface chemistry. Reagents are added so that the target mineral surfaces become water-repellent and attach to air bubbles that carry them into a froth. This approach is widely used for non-ferrous metal ores and sulfide ores such as copper, lead, zinc, and molybdenum. Froth flotation is also the usual route for hematite, where reverse flotation is the most proven method for upgrading, floating away silica gangue while iron minerals are suppressed. Magnetic separation exploits contrasts in magnetic susceptibility: magnetite is highly magnetic and easily concentrated through magnetic separation. Hematite is less magnetic and requires recovery through gravity separation, high-intensity magnetic separation, or flotation. Chromite processing often starts with gravity separation to remove the heavier chrome minerals before magnetic and flotation steps.

Smelting, hydrometallurgy and refining

Concentrates are converted to metal by high-temperature smelting or by aqueous chemistry, which is known as hydrometallurgy. Pyrometallurgical routes depend on the purity of the feed: iron concentrates must be controlled for impurities to meet blast furnace smelting requirements. Smelting is fuel- and electricity-intensive, and roasting sulfide concentrates releases sulfur dioxide, so emissions and energy use are central to plant design, and the carbon intensity of the energy supply largely determines the climate footprint of the metal produced. Hydrometallurgy dissolves the metal into a solution, often under controlled pressure and temperature. In one study of copper tailings, the process chain comprised leaching, solvent extraction and electrolysis, operating at moderate pressure and temperature. Solvent-extraction and electrowinning circuits trade heat demand for reagent consumption and solution management.

Tailings, acid mine drainage and rehabilitation

The residues of processing are a major environmental concern. The mining industry generates approximately 10 billion tons of tailings per year, tending towards doubling this amount by 2035. Tailings are a slurry of fine and coarse particles that are left over after the valuable portion of an ore is removed. Where the ore contains sulfide minerals, the residue can become acidic. Acid mine drainage arises from contact of mineral sulphides with water and oxygen, particularly in tailings dumps, waste and reef stockpiles, and underground mining voids. The AMD typically comprises dilute sulphuric acid, and has a pH in the range 2 to 6. When the acidic water is neutralized, iron can precipitate in an orange-yellow deposit known as "yellow boy", caused by the precipitation of iron oxide, iron hydroxide, or oxyhydroxides when the pH of the acidic water is raised. Not every tailings pile is equally hazardous; in one sample, pyrite occluded in silicates was present in modest amounts that posed little risk of acid generation.

Prevention targets the supply of oxygen and water. Methods include storing tailings in slurry form underwater to limit their exposure to dissolved oxygen, and flooding and sealing underground mines, along with reducing the contact with air, water, and bacteria through tailings covers. Backfilling mixtures of tailings and soil, crushed aggregate, sand and Portland cement is another way to limit acid formation. Once acid drainage exists, treatment typically neutralizes it, and lime is a common reagent. Some operations also recover metals from treatment sludge; one laboratory flowsheet recovered a mixed rare earth concentrate, achieving a purity of 80% by weight from the sludge generated during acid mine drainage treatment. Rehabilitation combines physical measures such as landform stabilization, covers, and drainage control with chemical and biological options, and recent reviews stress approaches that couple contaminant control with ecosystem function recovery.

Minerals in Industry, Technology and Energy

Construction is among the largest users of mineral raw materials by volume. Portland cement is made from a carefully proportioned mix in which limestone is the principal raw material, supplemented by materials containing silica, alumina, and iron. When the natural feed lacks one of these elements, corrective additions like iron ore, bauxite, or sand are blended in. The mix is burned in a rotary kiln at about 1,450 °C, where it aggregates at its sintering temperature. The resulting nodules, known as clinker, are finely ground with a small amount of gypsum. Gypsum is needed because it prevents flash setting caused by the very fast hydration of tricalcium aluminate. The powder is then mixed with sand, gravel and water to make concrete, the most widely used building material. Glass and ceramics draw on a different group of industrial minerals: silica sand and soda ash feed glass melts, while kaolin and feldspar-rich clays form the bodies of many ceramic products.

Mineral fertilizers are equally central to modern food production. Phosphorus is commonly supplied from phosphate fertilizers derived from phosphate rock, which is typically derived from phosphate rock and used in modern agriculture to enhance crop growth. Among plant nutrients, phosphorus is the second macronutrient most frequently limiting for plant growth after nitrogen, and more than 40% of cultivated soils are commonly deficient in P concentration. Efficiency is poor, however: plants benefit from only 20% of the applied chemical phosphorus fertilizers, and much of the remainder becomes locked in insoluble compounds in the soil. Commercial phosphate rock typically contains more than 30 percent P2O5. Processing it leaves a by-product, phosphogypsum, which contains radioactive contaminants; one estimate cited in a review states that only 15% of world phosphogypsum production is recycled as building products and asset retarder in the manufacture of Portland cement, while the rest is disposed of. Potash, the potassium-based fertilizer, supports crops in a different way: potassium is responsible for strengthening plant structure, improving water utilization, and enhancing resistance to diseases and stress.

Electronics and energy technology depend on a narrower set of elements. Silicon underpins the semiconductor devices used in computing and photovoltaic panels, and the International Energy Agency lists it among the essential minerals for a low-carbon system. Lithium, nickel, cobalt, manganese and graphite make up the core of the lithium-ion batteries that power portable devices and electric vehicles, and these are crucial to battery performance, longevity and energy density. Graphite is also used for anodes, and rare earth elements are essential for permanent magnets that are vital for wind turbines and EV motors. Copper, the key conductor for electricity networks, is a cornerstone for all electricity-related technologies.

The mineral demands of renewable-energy and electric vehicles differ in kind from those of fossil fuel systems. Fossil plants consume fuel continuously, whereas solar PV plants and wind farms do not require fuels to operate, they generally require more materials than fossil fuel-based counterparts for construction. The IEA estimates that a typical electric car requires six times the mineral inputs of a conventional car and an onshore wind plant requires nine times more mineral resources than a gas-fired plant of the same capacity. Because of this shift, since 2010 the average amount of minerals needed for a new unit of power generation capacity has increased by 50%. The IEA describes this as a shift from a fuel-intensive to a material-intensive system. Demand growth is expected to be steep: in a scenario that meets the Paris Agreement goals, the share of total demand rises significantly over the next two decades to over 40% for copper and rare earth elements, 60-70% for nickel and cobalt, and almost 90% for lithium.

Supply risk is shaped as much by geography as by volume. Mining and refining operations remain highly geographically concentrated, so rapid expansion can push prices up. Chile and Peru together mine more than a third of the world's copper, while Indonesia and the Philippines account for about half of global nickel production. The IEA also projects that the energy sector's overall needs for critical minerals could increase by as much as six times by 2040, depending on how rapidly governments act to reduce emissions.

Minerals in Human Nutrition and Health

Nutritional science groups the inorganic elements the body needs by the amount required each day. Macrominerals are defined as minerals that are required by adults in amounts greater than 100 mg/day, while trace elements are usually needed in amounts of 1–100 mg/day by adults. The classification concerns quantity rather than importance: a shortfall of a trace element can be as damaging as a shortfall of a major one. Seven macrominerals are conventionally recognized, namely calcium, phosphorus, magnesium, sodium, potassium, chloride and sulfur (the seven macrominerals are calcium, phosphorus, magnesium, sodium, potassium, chloride, and sulfur). The trace group includes nine elements, including iron, zinc, iodine, selenium, copper, manganese, fluoride, chromium, and molybdenum.

The macrominerals perform structural and regulatory work. Most of the body's calcium is locked into the skeleton and teeth, and the same ion also supports muscle contraction, nerve signalling and blood clotting. Phosphorus is a second skeletal component but also occurs in every cell, where it helps maintain acid-base balance. Magnesium participates in protein synthesis and in the function of muscles, nerves and the immune system. Sodium and potassium are the principal important to nervous system function and are the core of body fluid regulation, which is why they are discussed under electrolytes. Among trace elements, iron is a component of hemoglobin in red blood cells, and selenium acts together with vitamin E as an antioxidant that protects cells from oxidative damage. The body adjusts many of these levels by excreting surplus or absorbing more during digestion, although mineral deficiencies can occur depending upon a person's age, genetic disposition, or dietary deficiency.

Deficiency is most visible in iron. Iron deficiency is the most common cause of iron-deficiency anemia, a condition in which too few healthy red blood cells carry oxygen, producing fatigue, pallor and reduced work capacity. It is especially prevalent among young children, menstruating women and pregnant women, whose iron requirements are higher. Iodine deficiency is the best-documented example of a deficiency that is both preventable and widespread. Iodine is needed as the building block of thyroid hormones, which regulate metabolism and the development of the brain. Nearly 30% of the world's population has been estimated to have insufficient intake, and the WHO has recognized the resulting conditions as a major public health problem. Severe deficiency causes goiter, hypothyroidism and, in pregnancy, endemic goiter, hypothyroidism, cretinism, decreased fertility rate, increased infant mortality, and mental retardation. These effects are collectively termed iodine deficiency disorders. Toxicity is the reverse risk: excessive intake of minerals can lead to toxicity, with trace elements posing a particular risk.

Public health responses to these deficiencies are cheap and effective. Iodized salt was introduced in the United States in 1922 to address endemic goiter, and universal salt iodization, recommended by the World Health Organization (WHO), is the most effective public health measure to prevent iodine deficiency disorders. Food fortification and supplementation with oral iron tablets are the standard approaches to anemia, usually combined with dietary advice. Minerals are also used as medicines. Lithium, a light alkali metal, is an example. For the past 50 years, lithium has been the drug of choice for maintenance treatment of bipolar disorder, and it is effective in acute mania and long-term maintenance, although evidence for its efficacy in depression is modest. Its mechanism remains incompletely understood; it is thought to help strengthen nerve cell connections in brain regions that are involved in regulating mood, thinking and behavior. Because the margin between a therapeutic and a toxic blood level is narrow, lithium treatment requires regular monitoring of serum concentrations.

Some minerals are hazardous when inhaled or handled rather than eaten. Respirable crystalline silica, the quartz-based dust released by cutting, drilling, crushing and abrasive blasting, causes silicosis, a progressive scarring of the lungs, and increases the risk of tuberculosis and lung cancer. Fibrous silicate minerals known collectively as asbestos cause asbestosis, lung cancer and mesothelioma, a cancer of the pleural lining, typically after latency periods of decades. Occupational controls rely on a hierarchy of measures: engineering controls such as wet cutting, local exhaust ventilation and enclosure; respiratory protection; exposure monitoring against legal limits (in the United States, the permissible limit for respirable crystalline silica is 50 µg/m³ as an eight-hour time-weighted average); and medical surveillance of exposed workers. Many countries have banned asbestos use, and remediation of older buildings remains a major public health task.

Minerals in Culture, Art and Archaeology

Few natural materials have shaped human material culture as persistently as minerals. Colour, hardness, workability and scarcity determined whether a stone became a tool, a pigment, an ornament or a commodity moving along a trade route. Archaeology often recovers these uses before it recovers written records.

Gemstones and ornamental minerals

The cultural value of an ornamental mineral generally rests on three factors: how it is cut or polished, how scarce its sources are, and what meanings a society attaches to it. Lapis lazuli shows all three. Its deposits are concentrated in a few places, including Badakhshan in north-eastern Afghanistan and Chile in South America. Its significance was symbolic as well as material: Egyptian belief associated the stone with resurrection, and it was often embedded in amulets. Lapis also appeared in high-status burials, and excavated royal tombs at Ur, dated to roughly 2600 BC, held substantial lapis ornaments.

Cutting shapes value in a different way. Diamonds became culturally prized largely through faceting, and the brilliant cut, whose proportions were calculated by Marcel Tolkowsky in 1919, maximises the return of light from the stone. In East Asia, nephrite jade was carved into ritual and decorative objects for several thousand years, and turquoise was worked into jewellery and inlay across Mesoamerica and the American Southwest.

Pigments and dyes

Ochre, a natural earth rich in iron oxides and hydroxides, is among the oldest mineral materials used by humans. Red tones come mainly from hematite and yellow from goethite. Evidence of deliberate grinding and heating of ochre at Blombos Cave in South Africa, roughly 100,000 years old, points to early symbolic or practical preparation. Ochre later coloured the animal paintings in caves such as Lascaux and Altamira.

Copper minerals supplied other colours. Malachite, a green copper carbonate, was ground for use in Egyptian cosmetics and painting. Egypt also produced Egyptian blue, a calcium copper silicate made by heating raw materials, which is notable as one of the earliest synthetic pigments rather than a natural mineral. Lapis was the most expensive blue of antiquity. From the medieval Islamic period through the Renaissance, Badakhshan lapis was the principal source of the pigment ultramarine, produced by grinding the rock and refining the lazurite component through a labour-intensive process.

Flint, obsidian and early tools

Flint was the most widely used stone for tools in Neolithic Europe, and some of the best sources were mined. Grime's Graves in Norfolk, England, is one of ten known Neolithic flint mines in England and the only one open to visitors. Mining for flint began there in about 2650 BC, during the late Neolithic period. Miners dug shafts up to 13 metres deep to reach the finest black flint. They worked without metal: they used antler picks or stone axes to extract flint from the mines. The best black flint was prized because it looked glassy and flawless, much like the volcanic glass obsidian.

Obsidian, a natural volcanic glass, was knapped into blades and traded over long distances from sources such as central Anatolia and the Aegean island of Melos. Flint and obsidian were displaced slowly. Mining at Grime's Graves continued until about 1400 BC, and as bronze tools became more common and items of status, they started to eclipse traditional flint tools.

Bronze and Iron Age metallurgy and trade

Bronze is an alloy of copper and tin, typically with about ten per cent tin, and tin ore is far less common than copper. This scarcity drove long-distance exchange, and the Uluburun shipwreck off southern Turkey, dated to the late fourteenth century BC, carried copper and tin ingots alongside lapis and other luxury goods. Iron ore is abundant, but smelting and forging it required more specialised techniques, and iron gradually replaced bronze for many tools and weapons in the first millennium BC.

Trade networks linked distant regions well before the Iron Age. The lapis lazuli route to Central Asia is among the most significant trade routes of the ancient world, predating the Silk Road by millennia. Provenance studies confirm this. Chemical analysis indicated that Egypt had no local lapis deposits, and lapis found there has been traced to Badakhshan in Afghanistan.

History of Mineralogy as a Science

Long before mineralogy became a discipline, stones and metals were described mainly in practical and philosophical terms. Greek and Roman authors such as Theophrastus and Pliny the Elder wrote about stones and metals in encyclopedic treatises that mixed careful observation with inherited lore about medicinal and magical virtues. Medieval knowledge was carried largely by miners, assayers and smelters, and it survived in workshop practice more than in systematic texts. The Renaissance produced the first detailed technical manuals, of which Vannoccio Biringuccio's De la pirotechnia (1540) is a well-known example. These works recorded how to recognize ores, test them and smelt them, but they rarely attempted to sort minerals into a coherent scheme.

The decisive figure of the early period was Georgius Agricola (1494–1555), a physician who worked in German mining towns. Georgius Agricola (1494-1555) was a German scholar and scientist, dubbed "the father of mineralogy" for his contributions to the field. His first geological dialogue, Bermannus (1530), was his first contribution to geology. It covered the rise of the mining industry in Germany and the early development of the great mining centers in the region of the Erzgebirge. In De natura fossilium, Agricola presented a classification of minerals based on their physical properties and was likely the first to distinguish between simple substances and compounds. His posthumous De re metallica (1556) was the first full account of techniques of mining, separation, and purification of metals. To make his descriptions clear, Agricola made several hundred high-quality woodcuts. Agricola is generally counted among the first natural philosophers to rest their conclusions on observation rather than speculation, which marked a shift from inherited authority toward describing specimens directly.

Crystallography supplied the next foundation. Nicolaus Steno, the Danish-born anatomist and geologist, noted in 1669 that the angles between crystal faces stayed the same even when the crystals looked very different. Using drawings and two brief sentences, Stensen remarked that although crystals of quartz (silicon oxide) and hematite (iron oxide) appear in a great variety of shapes and sizes, the same interfacial angles persisted in every specimen. The French mineralogist Jean-Baptiste Romé de l'Isle later extended this idea across many substances. In his Cristallographie of 1783, Romé de l'Isle identified 450 crystal forms by which minerals crystallize. The goniometer that made such measurements practical was developed by his assistant Arnould Carangeot, who invented the goniometer in 1780. In 1784 René Just Haüy went further: he studied calcite crystals and found that they had the same shape, no matter what their size. Haüy hypothesized the existence of basic building blocks called integral molecules and argued that large crystals formed when many integral molecules bonded together. The constancy principle is now stated as the angles between the crystal faces of a given species are constant, whatever the lateral extension of these faces and the origin of the crystal, and are characteristic of that species.

The most transformative change came in 1912, when Max von Laue and his colleagues Walter Friedrich and Paul Knipping passed X-rays through crystals. Friedrich, together with student Paul Knipping, began experimenting on April 12, 1912, and found that the irradiation of a copper sulfate crystal with x-rays produced a regular pattern of dark points on a photographic plate placed behind the crystal. William Henry Bragg and his son William Lawrence Bragg quickly turned this effect into a method for locating atoms. In 1913 William H. Bragg and his son William L. Bragg determined the arrangement of atoms in sphalerite, ZnS, using data obtained with X-ray studies. For the first time, mineralogists knew the actual locations of atoms within a crystal. Before this, mineralogists were limited to examine the external form of minerals, their optical properties and their chemical composition. The Bragg equation, which describes when diffraction occurs from atomic planes, states that diffraction occurs only where the path difference equals an integral number of the X-ray wavelength. The Laue and Bragg work earned Nobel Prizes in 1914 and 1915, and it became the basis for X-ray diffraction, now a routine test used to identify the presence of different types of clay minerals.

The remaining decades of the twentieth century brought further tools and ideas. Electron microscopes allowed mineral textures and grain boundaries to be imaged at scales far finer than optical microscopy could resolve, while spectroscopic and microanalytical methods made it possible to measure composition in very small volumes. Thermodynamics, building on the phase rule that J. Willard Gibbs formulated in the 1870s, gave petrologists a quantitative basis for predicting which mineral assemblages are stable under given temperature and pressure. Together these developments changed mineralogy from a largely descriptive pursuit into a science of structure and equilibrium, and they reshaped classification around atomic arrangement and chemistry rather than external appearance alone, a transition discussed further in taxonomy and in the entry on geology.

Analytical Methods and Identification

Identification usually starts with X-ray powder diffraction (XRD). A ground sample scatters X-rays at different angles, and each crystalline phase produces a fixed set of lattice spacings, so its pattern works like a fingerprint that can be matched against reference data. Conversion of the diffraction peaks to d-spacings allows identification of the mineral because each mineral has a set of unique d-spacings. The method suits fine-grained material and intergrown mixtures that resist optical study, and if the sample is a mixture, XRD data can be analyzed to determine the proportion of the different minerals present. The peak pattern also reveals possible deviations of the minerals from their ideal compositions (presence of element substitutions and solid solutions), the structural state of the minerals (which can be used to deduce temperatures and (or) pressures of formation), and the degree of hydration.

Powder data cannot reliably reconstruct atomic arrangements. That task falls to single-crystal diffraction, which provides information necessary for determining a crystal's space group and the arrangement of atoms in a crystal's unit cell. Powder patterns are ambiguous for this purpose because different X-ray peaks correspond to different crystals in the powdered sample, and the data do not reveal the orientations of crystals or planes causing diffraction. Quantitative phase analysis relies on Rietveld refinement, which models the full pattern point by point, though it generally requires that a preliminary identification of mineral phases is performed before pattern modeling.

Chemical composition at the micrometre scale is measured with electron-beam instruments. The electron microprobe (EPMA) is commonly used to determine the compositions of mineral phases for geological samples, and it can analyze elements from boron to plutonium. Two detector types are used. Energy-dispersive spectrometry (EDS) is a relatively quick and simple process because the complete spectrum of energies is acquired simultaneously. Wavelength-dispersive spectrometry (WDS) acquires the spectrum sequentially as the full wavelength range is scanned. Although it takes longer to acquire a full spectrum, the WDS technique has much improved resolution compared to EDS. In a comparison on olivine, garnet, pyroxene, ilmenite and Cr-spinel, the two methods gave similar accuracy for major and minor components, but energy-dispersive spectrometry is inferior to wavelength-dispersive spectrometry for impurities and is completely inapplicable for still lower contents. Backscattered-electron images show compositional contrast, yet elements cannot be identified without characteristic X-rays. Quantified results depend on calibration, and certified standards of materials, minerals and metals are used in EPMA to calibrate the measurement of X-ray intensities for comparison with the sample of interest.

Optical microscopy of thin sections, which exploits refraction, birefringence and pleochroism under polarized light (discussed in the optical properties section), remains the first step for rock-forming minerals and shows their textures in place. Vibrational spectroscopy adds molecular information that optics cannot give. Raman spectroscopy measures laser light inelastically scattered by a sample and reveals bonds such as silicate, carbonate and sulfate groups; it needs little preparation and can be applied to grains only a few micrometres across under a microscope. Infrared spectroscopy measures absorption by vibrating groups such as $\mathrm{OH^-}$, $\mathrm{H_2O}$ and $\mathrm{CO_3^{2-}}$, which makes it sensitive to hydrous phases, carbonates and clays. The two are complementary: Raman is strong for symmetric bonds, while infrared is strong for polar groups.

Verification depends on reference resources. The International Mineralogical Association's Commission on New Minerals, Nomenclature and Classification (CNMNC) officially approves roughly 90 to 110 new species each year, and the list includes selected information on the 6079 currently valid species as of its September 2024 update. Later tallies differ by update date: one Wikipedia summary of the IMA-CNMNC list gives 6,226 valid minerals, including 1,153 pre-IMA minerals (grandfathered), and 97 questionable minerals. A name is usually considered secure only when several independent methods agree, for example a diffraction match, an EPMA composition consistent with the proposed formula, and a spectroscopic signature that matches a reference specimen.

Minerals Beyond Earth

Meteorites are the most accessible samples of extraterrestrial mineralogy. Carbonaceous chondrites, a primitive class of stony meteorites, contain hydrated silicates, magnetite, carbonates, sulfates and halite. Some of these minerals formed when liquid water altered their parent asteroids early in the Solar System's history. The least altered members have a bulk composition close to that of the Sun, apart from volatile elements. Calcium-aluminium-rich inclusions (CAIs) in meteorites such as Allende are among the oldest solids known. They condensed from the solar nebula, and isotopic evidence from short-lived radionuclides shows that some grains formed within a few million years of the nebula's isolation. Mineral assemblages in these meteorites therefore allow researchers to reconstruct early condensation sequences and the thermal and aqueous histories of their parent bodies.

Sample return missions have extended this record to asteroids. Samples from the carbonaceous asteroid Ryugu, returned by the Japanese Hayabusa2 spacecraft, are dominated by low-temperature secondary minerals formed through interaction with water, with rare anhydrous primary grains that crystallized in the hot inner disk. Small CAIs common in other carbonaceous chondrites are absent from Ryugu and CI chondrites, a difference that suggests their parent planetesimals formed farther from the Sun.

On the Moon, the Apollo program dominated the returned material, supplying about 382 kg of the roughly 384 kg of lunar rock brought to Earth before the Chinese Chang'e-5 mission. Mare basalts are composed mainly of pyroxene and plagioclase, with ilmenite prominent in titanium-rich varieties. Highland rocks are largely anorthosite, which is almost pure plagioclase. Fragments of highland crust found in Apollo 11 breccias were read as evidence for an early magma ocean, and the KREEP-enriched material in Apollo 14 breccias is linked to the final stages of that ocean's crystallization. Armalcolite, a titanium-bearing mineral, was first identified in Apollo 11 samples and named from the astronauts' surnames, and yoshiokaite was later described from the Apollo collection. Remote sensing of the lunar surface faces a limit: quartz and feldspar lack the transition-metal absorption features that visible and near-infrared spectroscopy relies on, so longer-wavelength infrared methods are being tested to map them.

Mars offers a different kind of record, built largely from orbital spectroscopy and rover analysis. Orbiters have identified three broad groups of hydrated minerals. According to NASA studies, phyllosilicates (clay minerals) formed more than 3.5 billion years ago where igneous rock was in prolonged contact with water, hydrated sulfates precipitated from evaporating, sometimes acidic, brines until about 3 billion years ago, and opaline silica is the youngest of the three. The CRISM spectrometer on the Mars Reconnaissance Orbiter detected clays around Endeavour crater, which guided the route of the Opportunity rover. Opportunity's traverse at Meridiani Planum confirmed sulfate and hematite deposits, and its landing site was chosen after orbital detection of hematite. The Curiosity rover, whose CheMin instrument performs X-ray diffraction on drilled samples, found clays in Gale crater. Analyses from the same crater indicate that some clays were later altered by sulfate-rich brines as the planet dried out, and iron carbonate found in sulfate-bearing layers suggests that a carbon cycle operated on ancient Mars.

Mineralogy also shapes how planetary surfaces are interpreted and how resources might be found beyond Earth. Spectral signatures from orbit are calibrated against meteorites and returned samples, which provide ground truth. Mineral assemblages indicate whether a site was once a lake, a hydrothermal system or an acidic evaporite basin, and those inferences guide landing-site selection and sampling strategy. Ilmenite on the Moon has been proposed as a source of iron and titanium for future settlements, which links planetary mineralogy to questions of in situ resource use.

Mineral Diversity, Discovery and Open Questions

The growing species list

The number of recognized mineral species keeps rising, and published totals differ by source and date. The IMA–CNMNC list gave 6,226 valid minerals, including 1,153 pre-IMA minerals (grandfathered), and 97 questionable minerals as of August 2026, while mindat.org listed 6,240 approved mineral species on its own page. The approval pace is steady: the commission approves on the order of 90 to 110 new species each year, and the figure rises to about 120 when name changes are counted. Over a shorter span, the total moved from about 4,300 in 2008 to 5413 officially recognized mineral species by November 2018.

Discovery is driven by two forces. The first is analytical capacity. Electron microprobes, X-ray diffraction on tiny single crystals and spectroscopic methods allow workers to separate small, intergrown or chemically unusual phases that earlier generations could not characterize, and many modern species are described from grains of only a few micrometres. The second is access to new environments. Deep mines, caves, fumaroles, hyperarid soils and meteorites all yield material that differs from familiar Earth-surface assemblages. A survey of meteorite occurrences, for example, identified 296 IMA-approved species that are known from material formed beyond Earth.

Nomenclature, discreditation and grouping

Naming is not a one-way process. Minerals described before 1959 were not approved through the modern procedure, and the IMA's approach was to let these names stand until someone checked them. As one commentator put it, the IMA allowed all previously accepted species to continue as accepted species until such time as someone discredited them, so many questionable names persist simply because nobody has re-examined the type material. Discreditation generally rests on two grounds: a mineral may be discredited if it is identical to another one that has priority, or if the name is misleading. The borishanskiite case is a typical priority example, since re-analysis of its holotype showed that it is identical to polarite, and because polarite has historical priority, borishanskiite is discredited.

Redefinition follows strict rules. A proposal must include a review of the literature on the mineral to be redefined, a re-examination of the type specimen, a comparison of the new data with the original, and justification for the redefinition, and the IMA prefers that such work be based on a study of type material. Even so, disagreements persist. A recent critique of a set of thiospinel redefinitions in the platinum-group elements argued that all four proposals for redefinition and discreditation should have been rejected if the full facts had been consulted and IMA-established guidelines had been adhered to.

The balance between splitting and lumping is shown clearly in the apatite group. Names for carbonate-bearing apatites have been repeatedly removed, because carbonate is never dominant and all carbonate-apatite species names have been discredited. Nomenclature revisions can also prevent unwieldy names: a new phosphate from Germany would have been named "hydrohydroxylmacraeite" under the old nomenclature, but the amendment for the Paulkerrite Group nomenclature has resulted in the approval of the name bergbauerite.

Unresolved questions about early and extreme environments

The history of mineral diversity is itself an open research area. Robert Hazen and colleagues proposed that Earth's mineral evolution can be divided into ten stages, each of which increased the mineral diversity of the planet. Their estimates for the earliest period are tentative. One study suggests that as many as 420 mineral species may have occurred during this early stage of Earth's mineral evolution, and later stages, which followed plate tectonics and produced hydrothermal deposits and high-pressure rocks, are estimated at perhaps 1500 species formed by purely physical and chemical processes. Many of these later minerals contain elements such as iron, copper and uranium that exist in more than one oxidation state, which helps explain the diversity.

The role of life is the most debated part of this history. The Great Oxygenation Event is one example of a biologically driven shift: driven by cyanobacterial photosynthesis, it changed chemical interactions with Earth substrates and transformed weathering, deposition and the availability of elements for biotic nature. Skeletal minerals provide another. The early Cambrian saw the abrupt rise of all major skeletal minerals, and few new types have appeared since then. How far such biological inputs shaped the global mineral inventory, and how much of the early Earth's mineralogy has been erased by recycling through the mantle, remain uncertain. Similar questions apply to deep-Earth phases that are difficult to sample and to mineral assemblages formed in extreme environments on the early Earth.

Predicting behaviour and linking structure to properties

A persistent challenge is predicting how minerals respond to changing temperature, pressure, water chemistry and biological activity. Species are distinguished by differences in chemical composition and crystal structure, but the same compound can form metastable phases, disordered intergrowths or polytypes whose stability depends on kinetics as much as on thermodynamics. Models that link atomic arrangements to macroscopic behaviour such as hardness, solubility, weathering rate or magnetic response are still incomplete, particularly for nanoscale and mixed-valence phases. Improving these links is central both to understanding planetary histories and to predicting how mineral reservoirs will behave under future environmental conditions.

Governance, Environment and Social Issues

Mineral rights and revenue transparency

Rights to explore for and extract minerals are usually set by national law, which may treat subsurface resources as state property and grant them to companies through licences or concessions. How the resulting revenue is shared among states, firms and local communities is a central governance question, and it is where the sovereignty of resource-rich states and the property rights of landholders often meet. The Extractive Industries Transparency Initiative (EITI), based in Oslo, seeks to establish a global standard for the governance of oil, gas and mineral resources. Its reporting requirements reach from how licenses and contracts are allocated and registered, who the beneficial owners of those operations are to how much is produced, paid and spent.

The effects of such disclosure are debated. An econometric study covering 1997 to 2014 found that EITI membership has had a significant and positive effect on economic development in member states, but the same study found that these gains had not yet produced measurable improvements in the control of corruption. A later analysis reached a similar conclusion: disclosure improved in many countries, while perceptions of corruption changed little.

Environmental impacts and tailings

Mining alters land, water and air in ways that can persist for decades. Waste rock, processing residues and tailings storage facilities carry the greatest risk of catastrophic failure. The collapse of a tailings dam at Brumadinho, Brazil, on 25 January 2019 led to the Global Tailings Review, co-convened in March 2019 by the United Nations Environment Programme (UNEP), Principles for Responsible Investment (PRI) and International Council on Mining and Metals (ICMM). Its outcome, the Global Industry Standard on Tailings Management, was launched in August 2020 and covers the entire tailings facility lifecycle – from site selection, design and construction, through management and monitoring, to closure and post-closure. The standard comprises 6 topic areas, 15 Principles and 77 auditable requirements, and it adds independent oversight and public disclosure. Its adoption depends on voluntary membership and on national legislation, which UNEP has offered to help governments incorporate.

Monitoring of water quality, biodiversity and air quality usually combines regulatory permits, baseline surveys, continuous sampling of discharges and groundwater, and independent audit. Acid mine drainage and dust can extend well beyond a mine's boundary, so the water cycle and local ecosystems are often the first receptors to show impacts.

Indigenous land claims and free, prior and informed consent

Many mining projects lie on lands that Indigenous peoples occupy or use. The main international instrument is ILO Convention 169, adopted in 1989. It is a legally binding international treaty requiring governments to consult with Indigenous and Tribal peoples in decision-making processes that affect them. Consultation is meant to be in good faith and in a form appropriate to the circumstances, with the objective of achieving agreement or consent, yet the Convention does not clearly require consent in every case. This gap explains why the wider principle of free, prior and informed consent (FPIC) has been adopted by other instruments, including the UN Declaration on the Rights of Indigenous Peoples and industry standards. Ratification remains limited: since 1989, only 23 countries have ratified the treaty. Court rulings have nonetheless given the principle practical force; in Guatemala, a 2014 appeals ruling held that the government must take into account the right to Free, Prior and Informed Consent when granting mining licenses on the lands of Indigenous communities. Industry certification schemes also apply the principle, and the Initiative for Responsible Mining Assurance (IRMA) standard states that new mines shall not be certified by IRMA unless they have obtained the free, prior and informed consent (FPIC) of potentially affected indigenous peoples.

International human rights frameworks such as the human rights obligations of states and the corporate responsibilities set out in the UN Guiding Principles shape how companies handle these claims. Cultural sites, burial grounds and sacred landscapes are often the most contested, and they are sometimes lost before any dispute is resolved. Mining can also have effects on cultural heritage that cannot be reversed by later rehabilitation.

Labour conditions and artisanal mining

Labour conditions vary widely between large industrial operations and small-scale or artisanal mining. In parts of central Africa, artisanal cobalt extraction has been linked to child labour, unsafe tunnelling and exposure to toxic dust, and it has prompted demands for supply-chain due diligence and traceability. Voluntary frameworks such as the Voluntary Principles on Security and Human Rights address the relationship between companies and public or private security forces at mine sites.

Sustainable supply, recycling and substitution

Critical minerals used in batteries, magnets, catalysts and electronics are increasingly managed through recycling and circular-economy strategies. Recycling can recover cobalt, nickel, lithium and rare earth elements from end-of-life products, but its economic and environmental value depends on collection rates, process energy and purity requirements. Life-cycle assessment is used to compare primary extraction with secondary recovery. Substitution, in which a less scarce material replaces a constrained one, is a further option, though it may shift demand to other mineral supply chains. Public policy has begun to set explicit goals for domestic extraction, processing and recycling of critical raw materials, as the European Union's Critical Raw Materials Act does, and trade rules, market concentration and supply and demand balances all shape how far such goals can be met.

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