Minerals and Rocks – Core Vocabulary

A comprehensive set of vocabulary flashcards covering minerals, igneous, sedimentary, and metamorphic rocks, their properties, formation processes, and the overarching rock cycle.

Mineral

A naturally occurring, inorganic solid with a definable chemical composition and an ordered crystalline structure.

Naturally Occurring Solid

A substance formed by geologic processes that is solid at Earth-surface temperatures; excludes synthetics, liquids, and gases.

Definable Chemical Composition

A fixed or narrowly ranged chemical formula that characterizes every specimen of a mineral, e.g., SiO₂ for quartz.

Crystalline Structure

An internal atomic arrangement that repeats in an orderly pattern, giving a mineral its crystal form and symmetry.

Typically Inorganic

Describes most minerals, which form from geologic—not biological—processes; biogenic minerals are noted exceptions.

Biogenic Mineral

A mineral precipitated by living organisms, such as calcite in shells or speleothems.

Calcite

A carbonate mineral (CaCO₃) common in limestone, marble, and cave formations.

Physical Properties (Minerals)

Observable traits—color, streak, luster, crystal habit, cleavage, hardness, etc.—used to identify minerals.

Color

The visible hue of a mineral in hand sample; often unreliable alone for identification.

Streak

The color of a mineral’s powdered form, tested by scraping on porcelain.

Luster

The way a mineral reflects light; categories include metallic, glassy, and earthy.

Crystal Habit

The typical external shape that crystals of a mineral display as they grow.

Cleavage

The tendency of a mineral to break along planes of weakness related to atomic structure.

Mohs Hardness Scale

Relative scale (1–10) ranking mineral resistance to scratching, with talc at 1 and diamond at 10.

Ionic Bond

Chemical bond produced by electron transfer between ions, common in salts like NaCl.

Covalent Bond

Strong bond formed by electron sharing between atoms, as in diamond.

Van der Waals Force

Weak electrostatic attraction between molecules; responsible for easy cleavage in graphite.

Silicate

Mineral group built from silica tetrahedra (SiO₄⁴⁻); composes >95 % of Earth’s crust.

Silica Tetrahedron

The four-oxygen, one-silicon pyramid that is the structural building block of all silicate minerals.

Oxide

Non-silicate mineral group with O²⁻ anion; e.g., hematite (Fe₂O₃).

Sulfide

Mineral group with S²⁻ anion; includes ore minerals like pyrite (FeS₂).

Sulfate

Mineral group containing SO₄²⁻; gypsum (CaSO₄·2H₂O) is typical.

Phosphate

Mineral group with PO₄²⁻ anion; fluorapatite (Ca₅(PO₄)₃F) is common in bones and teeth.

Carbonate

Minerals with CO₃²⁻, notably calcite (CaCO₃) and dolomite [CaMg(CO₃)₂].

Halide

Mineral group containing halogen ions (Cl⁻, F⁻); examples are halite (NaCl) and fluorite (CaF₂).

Igneous Rock

Rock formed by solidification of molten material (magma or lava).

Magma

Molten rock beneath Earth’s surface; may cool to form intrusive rocks.

Lava

Magma erupted onto Earth’s surface; cools to form extrusive rocks.

Geothermal Gradient

The rate of temperature increase with depth in Earth, influencing melting.

Decompression Melting

Partial melting triggered when hot mantle rock rises and pressure drops.

Addition of Volatiles

Process where water or CO₂ lowers a rock’s melting temperature, aiding magma generation.

Heat Transfer Melting

Generation of melt when rising magma heats and partially melts surrounding rock.

Viscosity

A magma’s resistance to flow; controlled by temperature, volatile content, and silica content.

Magmatic Differentiation

Processes (partial melting, assimilation, fractional crystallization) that create diverse igneous rocks from one magma source.

Partial Melting

Incomplete melting of a rock, producing silica-rich magma and mafic residue.

Assimilation

Incorporation of wall-rock pieces into magma, altering its composition.

Fractional Crystallization

Sequential removal of early-formed minerals from magma, changing remaining melt chemistry.

Volcanic (Extrusive) Rock

Igneous rock that crystallizes at or near the surface; generally fine-grained.

Plutonic (Intrusive) Rock

Igneous rock that cools slowly below ground; typically coarse-grained.

Composition (Igneous)

Overall chemical makeup of an igneous rock, linked to mineral content (felsic, intermediate, mafic, ultramafic).

Texture (Igneous)

Size, shape, and arrangement of crystals or glass in an igneous rock.

Bowen’s Reaction Series

Model describing the order of mineral crystallization from cooling magma.

Aphanitic Texture

Fine-grained igneous texture with crystals too small to see unaided; indicates rapid cooling.

Phaneritic Texture

Coarse-grained igneous texture with visible crystals; indicates slow cooling.

Sedimentary Rock

Rock formed by lithification of sediment or precipitation from solution.

Lithification

Compaction and cementation that transform loose sediment into solid rock.

Weathering

Physical, chemical, or biological breakdown of pre-existing rock at Earth’s surface.

Erosion and Transportation

Removal and movement of weathered material by wind, water, ice, or gravity.

Strata

Horizontal layers of sedimentary rock representing depositional episodes.

Clastic (Detrital) Rock

Sedimentary rock composed of fragments of pre-existing minerals/rocks, e.g., sandstone.

Carbonate Rock

Sedimentary rock formed by chemical or biological precipitation of carbonates; e.g., limestone.

Chert

Hard, microcrystalline quartz sedimentary rock often formed from silica-rich ooze.

Evaporite

Sedimentary rock (e.g., halite, gypsum) crystallized from evaporating water bodies.

Coal

Organic sedimentary rock formed from compressed plant material rich in carbon.

Metamorphic Rock

Rock altered in the solid state by heat, pressure, and chemically active fluids.

Protolith

The original, unmetamorphosed rock from which a metamorphic rock forms.

Metamorphic Grade

Intensity of metamorphism, increasing with temperature and pressure; indicated by index minerals.

Foliation

Planar alignment of platy minerals produced by differential stress during metamorphism.

Slate

Low-grade foliated metamorphic rock derived from shale; exhibits slaty cleavage.

Schist

Medium-grade foliated metamorphic rock rich in visible mica flakes.

Gneiss

High-grade foliated metamorphic rock with compositional banding of light and dark minerals.

Marble

Nonfoliated metamorphic rock formed from limestone; composed mainly of calcite.

Quartzite

Nonfoliated metamorphic rock formed from quartz-rich sandstone; extremely hard.

Rock Cycle

Continuous set of processes that transform rocks among igneous, sedimentary, and metamorphic types.

Plate Tectonics (and Rock Cycle)

Global mechanism driving rock-forming processes—melting, uplift, burial—through interactions at plate boundaries.