Mineralogy Glossary

Bravais Lattice

One of 14 distinct three-dimensional lattice types that describe all possible periodic arrangements of points …

Crystal Face

A flat, planar surface on a natural crystal that reflects an internal plane of atoms. …

Crystal Habit

The characteristic external shape or form of a mineral crystal, described by terms such as …

Crystal System

One of seven categories of crystal symmetry (cubic, hexagonal, trigonal, orthorhombic, tetragonal, monoclinic, triclinic) defined …

Crystal Zone

A set of crystal faces whose intersecting edges are all parallel to a common direction …

Enantiomorphism

The property of a crystal structure that exists in two mirror-image forms (like left and …

Epitaxy

The oriented overgrowth of one crystalline material on the surface of another, with a specific …

Miller Indices

A notation system using three integers (hkl) to describe the orientation of crystal faces and …

Point Group

The set of symmetry operations (rotation, reflection, inversion) that describe the macroscopic symmetry of a …

Polymorphism

The ability of a chemical compound to crystallize in more than one crystal structure. Diamond …

Pseudomorph

A mineral that has the external form of another mineral species, formed by chemical replacement …

Space Group

A mathematical description of the full symmetry of a crystal structure, combining point symmetry with …

Symmetry Element

A geometric element (axis, plane, center) with respect to which one or more symmetry operations …

Twinning

The intergrowth of two or more crystal individuals in a symmetrical relationship, producing contact twins, …

Unit Cell

The smallest repeating structural unit of a crystal lattice that, when repeated in all directions, …

Cleavage

The tendency of a mineral to break along flat planar surfaces determined by its crystal …

Density

The mass per unit volume of a mineral, typically expressed in grams per cubic centimeter. …

Electrical Conductivity

The ability of a mineral to conduct electrical current. Native metals and graphite are good …

Fracture

The way a mineral breaks when not along cleavage planes. Types include conchoidal (shell-like), uneven, …

Fusibility

The ease with which a mineral melts when heated, rated on the von Kobell scale …

Magnetism

The property of being attracted to a magnet, due to iron or other ferromagnetic elements …

Mohs Hardness

A relative scale of mineral hardness from 1 (talc) to 10 (diamond), based on scratch …

Phosphorescence

The continued emission of visible light by a mineral after the exciting radiation source has …

Radioactivity

The emission of ionizing radiation by minerals containing unstable isotopes of uranium, thorium, or other …

Specific Gravity

The ratio of a mineral's weight to the weight of an equal volume of water. …

Streak

The color of a mineral's powder, typically observed by rubbing the mineral across an unglazed …

Tenacity

A mineral's resistance to bending, breaking, crushing, or tearing. Terms include brittle, malleable, ductile, sectile, …

Thermal Conductivity

The rate at which a mineral transmits heat. Diamond has exceptionally high thermal conductivity; many …

Triboluminescence

The emission of light when a mineral is scratched, crushed, or rubbed. Sphalerite and fluorite …

Adularescence

The billowing, floating light effect seen in moonstone (orthoclase/albite), caused by light scattering from thin …

Asterism

The star-like optical phenomenon seen in certain cabochon-cut minerals, produced by light reflecting from oriented …

Aventurescence

A glittery, sparkling optical effect caused by reflections from flat, oriented platelets of a contrasting …

Birefringence

The splitting of a light ray into two polarized rays when passing through an anisotropic …

Chatoyancy

The cat's-eye effect seen in certain cabochon-cut minerals, caused by parallel fibrous inclusions or hollow …

Dispersion

The separation of white light into spectral colors as it passes through a mineral, caused …

Fluorescence

The emission of visible light by a mineral when exposed to ultraviolet radiation. Named after …

Labradorescence

The iridescent play of color seen in labradorite feldspar, caused by interference of light from …

Luster

The quality and intensity of light reflected from a mineral's surface. Major types include metallic, …

Opalescence

A milky, iridescent light effect caused by the scattering of light from very fine particles …

Play of Color

The spectral iridescence displayed by precious opal, caused by the diffraction and interference of light …

Pleochroism

The property of showing different colors when viewed along different crystallographic directions, caused by differential …

Refractive Index

A measure of how much light slows down and bends when passing through a mineral, …

Schiller Effect

A metallic, bronzy iridescence caused by reflection from thin oriented exsolution lamellae or platelet inclusions …

Transparency

The degree to which light passes through a mineral: transparent (clear), translucent (light passes but …

Contact Metamorphism

Metamorphism caused by heat from an igneous intrusion affecting the surrounding country rock. Produces calc-silicate …

Evaporite

Minerals deposited from the evaporation of saline water bodies. Common evaporite minerals include halite, gypsum, …

Gossan

The iron-rich, oxidized cap of a sulfide ore deposit formed by weathering. Often contains secondary …

Hydrothermal

Formed from hot, mineral-rich fluids circulating through fractures in rock. A major source of metallic …

Igneous

Formed from the cooling and crystallization of molten magma or lava. Minerals crystallize in a …

Laterite

A soil and rock type rich in iron and aluminum oxides (goethite, gibbsite), formed by …

Metamorphic

Formed or transformed by heat, pressure, or chemically active fluids within the Earth's crust, without …

Metasomatism

The process of chemical alteration of a rock by hydrothermal fluids, involving the introduction or …

Pegmatite

Extremely coarse-grained igneous rocks that form from the last residual fluids of a crystallizing magma. …

Pneumatolysis

Mineral formation or alteration by hot gases and vapors emanating from a cooling magma. Responsible …

Regional Metamorphism

Large-scale metamorphism resulting from elevated temperature and pressure over wide areas, typically associated with mountain-building …

Sedimentary

Formed at or near the Earth's surface through precipitation from water, biological activity, or weathering …

Supergene Enrichment

The process by which downward-percolating groundwater dissolves metals from oxidized surface zones and re-deposits them …

Acid Test

A simple field test using dilute hydrochloric acid to identify carbonate minerals. Calcite fizzes vigorously; …

Blowpipe Test

A traditional flame-based field test in which a narrow jet of air is directed onto …

Borax Bead Test

A traditional identification test in which a mineral is dissolved in a molten borax bead …

Dana Classification

An alternative mineral classification system based on crystal chemistry and structure, developed by James Dwight …

Electron Microprobe

An instrument that bombards a mineral sample with electrons to generate characteristic X-rays, allowing precise …

Flame Test

A test in which a mineral is introduced into a flame to identify characteristic colors …

Locality

A specific geographic site where minerals are found. Famous localities (Tsumeb, Minas Gerais, Dal'negorsk) are …

Magnetic Separation

A physical technique used to separate magnetic minerals (magnetite, pyrrhotite) from non-magnetic minerals using a …

Matrix

The host rock in which a mineral specimen is embedded. Specimens on matrix are often …

Paragenesis

The characteristic association of minerals that formed together under the same geological conditions, useful for …

Raman Spectroscopy

A non-destructive analytical technique using laser light to identify minerals by their molecular vibration signatures. …

Thin Section

A slice of rock or mineral ground to 0.03 mm thickness and mounted on glass …

Type Locality

The geographic location where a mineral species was first discovered and described. Important for establishing …

UV Fluorescence Test

Examination of a mineral under shortwave (254 nm) and/or longwave (365 nm) ultraviolet light to …

XRD

X-ray diffraction, a technique used to identify minerals by their crystal structure. X-rays are diffracted …

Asterism (Gem)

The star-shaped optical phenomenon in star rubies, star sapphires, and star garnets, caused by oriented …

Brilliance

The white light returned from the interior and surface of a faceted gemstone to the …

Cabochon

A gemstone cutting style producing a smooth, domed top and flat or slightly convex back, …

Carat

The unit of weight for gemstones, equal to 0.2 grams. One carat is divided into …

Chatoyancy (Gem)

The mobile bright band seen in cat's-eye gems such as chrysoberyl cat's-eye, caused by reflection …

Clarity

A grading measure of the absence of inclusions and blemishes in a gemstone. The GIA …

Color Zoning

Uneven distribution of color within a gemstone, often in distinct bands or patches reflecting growth …

Crown

The upper portion of a faceted gemstone, above the girdle. Crown height and angle affect …

Cut Grade

An assessment of how well a gemstone has been fashioned, evaluating proportions, symmetry, and polish. …

Dispersion (Gem)

The difference in refractive index between red and violet light in a gemstone, quantified as …

Facet

A flat, polished surface deliberately cut on a gemstone to reflect and refract light. The …

Fire

The display of spectral colors (red, orange, yellow, green, blue, violet) produced by the dispersion …

Girdle

The narrow band around the widest part of a faceted gemstone, separating the crown from …

Inclusion

Any internal feature within a gemstone, including crystals, needles, clouds, feathers, or growth irregularities. Inclusions …

Loupe

A small magnifying lens used by gemologists to examine stones. Standard gem loupes are 10× …

Pavilion

The lower portion of a faceted gemstone, below the girdle. The pavilion angle is critical …

Pleochroism (Gem)

The display of different colors in different crystallographic directions, important in gem cutting decisions. Tanzanite …

Refractive Index (Gem)

A key gemological property measured with a refractometer to help identify gem species. Values range …

Table

The largest and topmost flat facet on a faceted gemstone. The table percentage (table width …

Treatment

Any process applied to a gemstone to improve its appearance or durability after mining. Common …

Arsenate

Minerals containing the arsenate anion (AsO₄³⁻), typically forming in the oxidized zones of arsenic-bearing ore …

Borate

Minerals containing boron and oxygen as the dominant anionic complex. Borates are concentrated in evaporite …

Carbonate

Minerals containing the carbonate anion (CO₃²⁻). The carbonate class includes calcite (CaCO₃), dolomite (CaMg(CO₃)₂), malachite, …

Chromate

Minerals containing the chromate anion (CrO₄²⁻). Crocoite (PbCrO₄) is the most famous chromate mineral, known …

Cyclosilicate

A silicate mineral subclass in which SiO₄ tetrahedra link into closed rings, typically three-membered (Si₃O₉) …

Halide

Minerals in which a halogen element (fluorine, chlorine, bromine, iodine) is the dominant anion. Examples …

Hydroxide

Minerals containing the hydroxyl anion (OH⁻) as the dominant group. Includes goethite (FeOOH), brucite (Mg(OH)₂), …

Molybdate

Minerals containing the molybdate anion (MoO₄²⁻). Wulfenite (PbMoO₄) is the most collectable molybdate, prized for …

Native Element

Minerals consisting of a single element in uncombined form. The native element class includes native …

Nitrate

Minerals containing the nitrate anion (NO₃⁻), found mainly in arid regions. Niter (KNO₃) and soda …

Oxide

Minerals formed by direct combination of a cation with oxygen, without additional complex anions. Includes …

Phosphate

Minerals containing the phosphate anion (PO₄³⁻). Includes the apatite group, turquoise, lazulite, monazite, and many …

Silicate

The largest mineral class, defined by the presence of SiO₄ tetrahedra as the fundamental building …

Sorosilicate

A silicate mineral subclass in which SiO₄ tetrahedra are linked in pairs sharing one oxygen, …

Sulfate

Minerals containing the sulfate anion (SO₄²⁻). Common sulfates include gypsum (CaSO₄·2H₂O), barite (BaSO₄), celestine (SrSO₄), …

Sulfide

Minerals containing sulfur as the dominant anion bonded to metals. The sulfide class includes major …

Tectosilicate

A silicate mineral subclass in which every SiO₄ tetrahedron shares all four oxygen atoms with …

Telluride

Minerals containing tellurium as the dominant anion combined with metals. Gold tellurides such as calaverite …

Tungstate

Minerals containing the tungstate anion (WO₄²⁻). Important tungstate minerals include scheelite (CaWO₄), which fluoresces bright …

Vanadate

Minerals containing the vanadate anion (VO₄³⁻), often forming brightly colored secondary minerals in oxidized ore …

Alluvial

Relating to material deposited by flowing water. Alluvial mineral deposits form in river channels and …

Assay

The chemical analysis of an ore sample to determine the content of valuable metals or …

Beneficiation

The process of treating ore to increase the concentration of valuable minerals by removing gangue. …

Deposit

A natural accumulation of a mineral or minerals in a specific location, implying sufficient concentration …

Eluvial

Relating to material that has weathered and concentrated in place without being transported by water. …

Flotation

A mineral processing technique that selectively separates minerals by exploiting differences in their surface hydrophobicity. …

Gangue

The commercially valueless rock or minerals associated with an ore in a mineral deposit. Common …

Grade

The concentration of valuable minerals or metals in an ore, expressed as grams per tonne …

Greisen

A hydrothermally altered granitic rock composed mainly of quartz and mica (usually muscovite or lepidolite), …

Lode

A vein or system of veins containing metallic ore, or more broadly any continuous ore-bearing …

Open Pit

A surface mining method in which ore is extracted from a large, open excavation in …

Ore

A naturally occurring rock or mineral from which a valuable constituent, typically a metal, can …

Overburden

The waste rock and soil overlying a mineral deposit that must be removed before or …

Placer

A mineral deposit formed by the mechanical concentration of heavy, resistant minerals (gold, cassiterite, diamond, …

Skarn

A metasomatic rock formed at the contact between an igneous intrusion and carbonate host rock, …

Smelting

The pyrometallurgical process of extracting a metal from its ore by heating it in a …

Stockwork

A mineral deposit consisting of a network of small, irregular, closely spaced veins and veinlets …

Tailings

The waste material remaining after valuable minerals have been extracted from ore during processing. Tailings …

Underground Mining

Mining methods that extract ore from below the surface through shafts and tunnels. Used for …

Vein

A tabular body of minerals filling a fracture or fault in host rock, typically formed …

Acid Mine Drainage

Acidic, metal-rich water produced when sulfide minerals (especially pyrite) are exposed to air and water …

Alteration

Mineralogical and chemical changes in a rock caused by hydrothermal fluids, weathering, or metamorphism. Hydrothermal …

Asbestiform

Referring to minerals that occur as long, thin, flexible fibers, a growth habit that makes …

Authigenic

Describing minerals that formed in place within a sediment or rock, rather than being transported …

Bioleaching

The use of microorganisms (especially acidophilic bacteria like Acidithiobacillus ferrooxidans) to extract metals from low-grade …

Biomineralization

The process by which living organisms produce minerals, often to form shells, bones, or teeth. …

Diagenesis

Post-depositional changes to sediments at low temperature and pressure, including compaction, cementation, recrystallization, and dissolution. …

Efflorescence

The formation of a powdery or crusty deposit of salts or secondary minerals on a …

Hypogene

Referring to minerals or processes originating from deep below the surface, typically involving ascending hydrothermal …

Oxidation Zone

The near-surface zone of a sulfide ore deposit where primary sulfides have been chemically altered …

Patina

A surface layer formed on a mineral or rock by long-term exposure to air, water, …

Remediation

The process of removing or neutralizing contamination from soils or water affected by mining or …

Secondary Mineral

A mineral formed by the alteration, weathering, or metamorphism of a pre-existing primary mineral. Secondary …

Supergene

Referring to processes and minerals formed near the Earth's surface by downward-percolating meteoric water. Supergene …

Weathering

The physical disintegration and chemical decomposition of minerals and rocks exposed at the Earth's surface. …

Birthstone

A gemstone traditionally associated with each month of the year. The modern birthstone list was …

Cameo

A form of relief carving in a layered stone (typically onyx, sardonyx, or shell) where …

Discredited Mineral

A mineral name that has been officially rejected by the IMA because it was found …

Holotype

The single physical specimen designated as the name-bearing type of a mineral species at the …

IMA Approval

The formal recognition of a new mineral species by the International Mineralogical Association's Commission on …

Intaglio

The opposite of cameo: a carving technique in which the design is incised below the …

Lapidary

The art and practice of cutting, shaping, and polishing gemstones and ornamental stones. A lapidary …

Lectotype

A specimen selected from the original material examined by the author of a mineral species …

Luminescence

The emission of light by a mineral by any means other than incandescence (heat). Types …

Piezoelectricity

The generation of electric charge by mechanical deformation of certain crystals, discovered in quartz by …

Pyroelectricity

The generation of a temporary electric potential in certain crystals when heated or cooled, due …

Strunz Classification

The mineralogical classification system devised by Karl Hugo Strunz in 1941, organizing minerals into ten …

Thermoluminescence

The emission of light from a mineral when heated, caused by the release of electrons …

Type Specimen

A specific physical specimen held in a museum collection that serves as the definitive reference …

Variety

A named subdivision of a mineral species distinguished by color, habit, or minor compositional variation, …