Geology Chapters 5–8 and Interludes: Minerals, Rocks, Weathering, and Metamorphism

Comprehensive vocabulary flashcards covering mineralogy, igneous geology, weathering and soil science, sedimentary processes, and metamorphic petrology based on course lecture notes.

Mineralogist

A geoscientist specializing in the study of minerals.

Mineral

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

Crystalline Material

A substance in which atoms are arranged in an ordered crystalline lattice.

Biogenic minerals

Minerals created by living organisms, such as vertebrate bones and teeth, or oyster, mussel, and clam shells.

Unit Cell

The smallest group of atoms making up a mineral's unique pattern that produces the shape of the crystal.

Crystal

A single, continuous piece of crystalline solid typically bounded by flat crystal faces that grow naturally as the mineral forms.

Diffraction

The splitting of light into many tiny beams that interfere with one another, occurring when waves interact with regularly spaced objects whose spacing approaches the wavelength of the waves.

Polymorph

Two or more minerals that possess the same chemical composition but have different internal crystalline structures (e.g., diamond and graphite).

Solid-state diffusion

The movement of atoms or ions through a solid to arrange into a new crystal structure without melting having occurred, taking place very slowly when a solid is heated and/or compressed.

Biomineralization

The process by which living organisms cause minerals to precipitate either within or on their bodies, or immediately adjacent to their bodies.

Euhedral

A mineral crystal grown in an open cavity with well-developed, distinct crystal faces.

Anhedral

A mineral crystal grown in a confined, tight space, preventing the development of distinct crystal faces.

Streak

The color of a powder produced by crushing or scraping a mineral with a hardness $< 6$ across unglazed porcelain.

Luster

The way a mineral surface scatters light, classified into metallic and nonmetallic categories.

Hardness

A measure of the relative ability of a mineral to resist scratching, representing the resistance of bonds in the crystal structure to breaking.

Mohs hardness scale

A relative sequence of ten reference minerals used to compare mineral scratch hardness: talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum, and diamond.

Specific Gravity

The density of a mineral represented by the ratio of mineral weight relative to the weight of an equal volume of water.

Crystal habit

The general outward shape of an individual crystal or aggregate cluster of crystals that grew unimpeded, reflecting internal atomic structure.

Cleavage

The tendency of a mineral to break along preferred planes where atomic bonding is weakest.

Conchoidal fracture

Smoothly curving, clamshell-shaped fracture surfaces along which materials that lack cleavage planes break.

Silica tetrahedron

A fundamental anionic building block consisting of four oxygen atoms surrounding a single central silicon atom ($\text{SiO}_4^{4-}$).

Rock

A coherent, naturally occurring solid aggregate of minerals or a body of glass.

Clastic rocks

Sedimentary rocks composed of cemented-together detritus derived from the weathering of preexisting rock.

Crystalline rocks

Rocks consisting of minerals that grew and interlocked like pieces of a jigsaw puzzle when a melt solidified.

Bedrock

Solid rock that remains intact and attached to the Earth's crust.

Outcrop

An exposure of bedrock at the Earth's surface.

Thin Section

A $0.03\,\text{mm}$-thick slice of rock mounted on a glass plate and examined under a petrographic microscope using polarized and non-polarized light.

Extrusive igneous rocks

Igneous rocks that cool and solidify rapidly at or near the Earth's surface, resulting in fine-grained crystals or pyroclastic debris.

Intrusive igneous rocks

Igneous rocks that cool slowly at depth below the Earth's surface, allowing large mineral crystals to grow.

Geotherm

The curving line on a graph representing the change in temperature with increasing depth within the Earth.

Decompression melting

Melting that occurs when upward-moving mantle rock experiences a drop in pressure while maintaining a high temperature.

Flux melting

The melting of hot mantle rock triggered by the addition of volatile materials (such as $\text{H}_2\text{O}$), which break chemical bonds and lower the rock's melting temperature.

Heat transfer melting

The melting of crustal rock caused by heat conducted from rising, hot mantle magma.

Partial melting

The incomplete melting of a rock where minerals with the lowest melting temperatures melt first, producing a melt more felsic and silica-rich than the source rock.

Assimilation

The contamination of magma caused when blocks of country rock fall into the magma chamber and dissolve.

Magma mixing

The process by which different magmas from separate sources enter the same chamber and mutually dissolve or mix to form an intermediate composition.

Viscosity

A fluid's resistance to flow, which decreases with higher temperature, lower silica content, and higher volatile content.

Fractional Crystallization

The sequential crystallization and separation of minerals as magma cools, progressively enriching the remaining melt in silica, aluminum, sodium, and potassium.

Dike

A tabular igneous intrusion that cuts vertically or obliquely across preexisting layering in the host country rock.

Sill

A nearly horizontal, tabular igneous intrusion injected parallel between layers of country rock.

Laccolith

A blister-shaped igneous intrusion formed when magma injected between layers accumulates and pushes overlying strata upward into a dome.

Pluton

An irregular or blob-shaped intrusive body ranging from tens of meters to tens of kilometers across.

Batholith

A vast composite intrusive igneous rock body up to several hundred kilometers long and $100\,\text{km}$ wide, formed by numerous coalesced plutons.

Xenolith

A stoped relict block of wall rock enclosed within an intrusive igneous rock after the magma freezes.

Aphanitic

A fine-grained igneous rock texture produced by rapid cooling under extrusive conditions.

Phaneritic

A coarse-grained igneous rock texture with visible crystals produced by slow cooling within intrusive environments.

Porphyritic

An igneous texture containing both large crystals (phenocrysts) and a fine-grained groundmass, reflecting a two-stage cooling history.

Large igneous province

A region in which massive volumes of low-viscosity mafic lava or ash erupted over a relatively short interval of geologic time.

Flood Basalts

Vast sheets of low-viscosity basaltic lava that erupt from fissures and spread over extensive land surfaces.

Sediments

An accumulation of loose, uncemented mineral grains, rock clasts, shell fragments, or precipitated crystals.

Weathering

The combination of surface processes that break up and chemically corrode solid rock, converting it into sediment.

Jointing

Natural cracks that develop in rock due to cooling, contraction, and expansion during exhumation and pressure release.

Talus

A sloping apron of angular fallen rock blocks accumulated along the base of a cliff.

Frost Wedging

A physical weathering process occurring when water trapped in cracks freezes, expands by about $9\%$, and wedges the fracture open.

Salt Wedging

A physical weathering process in arid climates where dissolved salts precipitate in rock pores and push grains apart.

Dissolution

A chemical weathering process in which minerals dissolve into separated ions within a water solution.

Hydrolysis

A chemical weathering reaction in which water molecules chemically react with silicate minerals, breaking them down into clays and other minerals.

Spheroidal Weathering

A weathering phenomenon where joint-bounded blocks weather faster at corners and edges, causing the rock to spall into concentric shells and become rounded.

Differential Weathering

The unequal rate of weathering across different rock layers in an outcrop, producing stair-step cliffs or ledges.

Soil

Surface sediment modified through reactions with rainwater, air, and the addition of organic debris to form distinct horizons.

Zone of leaching

The upper soil/regolith layer where downward-percolating rainwater dissolves ions and washes away fine clay particles.

Zone of Accumulation

The subsurface soil layer where descending water precipitates new minerals and deposits its load of fine clay.

Humus

Decomposed, dark organic matter within a soil profile derived from decayed plant and animal tissues.

Regolith

The layer of loose, fragmented rock, unconsolidated mineral grains, and dust covering solid bedrock.

Laterite

A hard, brick-red, heavily leached soil enriched in insoluble iron and aluminum oxides that forms in warm, wet tropical environments.

Loam

A fertile soil consisting of roughly equal proportions of sand, silt, and clay.

Lithification

The collective mechanical and chemical transformation of loose sediment into solid sedimentary rock via compaction and cementation.

Breccia

A coarse-grained clastic sedimentary rock consisting of angular rock fragments that have experienced minimal transport.

Conglomerate

A coarse-grained clastic sedimentary rock containing rounded pebbles and cobbles smoothed by water transport.

Arkose

A feldspar-rich sandstone typically deposited in alluvial fans close to a granitic source under arid conditions.

Alluvial Fan

A cone- or wedge-shaped apron of poorly sorted gravel, sand, and sediment deposited where a steep mountain stream empties onto a flat valley plain.

Cross bedding

Internal sedimentary laminations inclined at an angle to the main horizontal bedding boundary, formed along the migrating slip faces of ripples or sand dunes.

Graded beds

Sedimentary layers displaying a progressive upward decrease in clast size from coarse material at the base to fine mud at the top, deposited by waning turbidity currents.

Mud Cracks

Polygonal fracture patterns formed on fine-grained sedimentary bed surfaces as muddy sediments dry and shrink.

Sedimentary basin

A low-lying crustal depression created by regional subsidence that accumulates thick sequences of sediment.

Transgression

The landward migration of the shoreline and its associated depositional belts resulting from a relative rise in sea level.

Regression

The seaward migration of a shoreline and associated sedimentary environments caused by a relative fall in sea level.

Diagenesis

All physical, chemical, and biological alterations that transform sediment into sedimentary rock and modify the rock after formation, prior to metamorphism.

Protolith

The preexisting parent rock from which a metamorphic rock forms through changes in temperature, pressure, stress, or fluid interaction.

Recrystallization

A metamorphic process that changes the size and shape of mineral grains without altering the chemical composition or identity of the minerals.

Neocrystallization

The growth of new metamorphic minerals as chemical reactions digest the unstable minerals of the protolith.

Pressure Solution

A process where mineral grains dissolve along edges bearing the highest compressive stress, with dissolved ions migrating and reprecipitating in lower-pressure spaces.

Plastic Deformation

The permanent ductile changing of mineral grain shapes without brittle fracturing under elevated temperatures and differential stress.

Metasomatism

The substantial alteration of a rock's overall chemical composition caused by ion exchange with circulating hydrothermal fluids during metamorphism.

Slate

A very fine-grained, low-grade foliated metamorphic rock derived from shale that readily cleaves into thin, flat roofing sheets.

Phyllite

A fine-grained foliated metamorphic rock characterized by a satiny, silky luster caused by the preferred alignment of fine white mica crystals.

Schist

A medium- to coarse-grained foliated metamorphic rock possessing visible, aligned mica flakes defining schistosity.

Migmatite

A mixed metamorphic and igneous rock formed when high-grade conditions cause partial melting of felsic bands while mafic bands remain solid.

Metamorphic Facies

A specific suite of metamorphic mineral assemblages that develop under a characteristic range of pressure and temperature conditions.

Prograde Metamorphism

Metamorphic changes taking place as temperature and pressure progressively rise, driving off volatile water molecules to produce progressively drier rocks.

Retrograde metamorphism

Metamorphism that occurs under decreasing pressure and temperature conditions as deep rocks return toward the surface, requiring hydrothermal fluid entry to rehydrate minerals.

Isograd

A map line that marks the first visible geographic appearance of a specific index mineral, delineating the boundary of a metamorphic zone.

Metamorphic aureole

A halo or belt of contact-metamorphosed rock that surrounds an igneous intrusion.

Thermal metamorphism

Metamorphism driven primarily by heat conducted into country rock from an intruding igneous magma body, occurring without significant differential stress.

Dynamic metamorphism

Metamorphism that takes place along fault zones under intense shear stress, ductilely stretching and smearing mineral grains to form mylonite.

Regional metamorphism

Large-scale metamorphism driven by intense heating, burial, and directional tectonic compression across broad mountain-building collision belts (orogenesis).

Rock cycle

The progressive transformation of Earth materials through geologic processes from one rock class (igneous, sedimentary, metamorphic) to another.

Bowen's reaction series

A schematic model showing the progressive crystallization sequence of silicate minerals from cooling magma through distinct continuous and discontinuous branches.

Sheet silicates

A mineral group in which tetrahedra share three oxygen atoms to produce two-dimensional layers with one direction of perfect cleavage, exemplified by biotite and muscovite.

Framework silicates

A mineral group where each silica tetrahedron shares all four oxygen atoms within a three-dimensional lattice, exemplified by quartz and feldspars.