Geology: Igneous, Sedimentary, and Metamorphic Rocks & Processes Flashcards

Vocabulary flashcards covering metamorphic rocks, sedimentary rock classification, weathering and soil science, volcanic processes, and igneous geology.

Metamorphism

The change in a rock's mineralogy and/or texture in response to heat and pressure, usually in the presence of fluids.

Confining Pressure

A force applied equally in all directions on a rock that increases with depth and causes a reduction in volume.

Directed Pressure

A force applied with greater intensity in a particular direction, causing deformation, shape change, and preferred mineral orientation.

Pressure Solution

A metamorphic process where mineral grains dissolve at sites of high directed pressure and reprecipitate or grow in areas of lower stress.

Contact Metamorphism

Thermal alteration of rocks at or near contact with a body of intruding magma, producing non-foliated rocks such as hornfels without directed pressure.

Regional Metamorphism

Large-scale metamorphism occurring over broad areas in mountain belts and island arcs at convergent boundaries, driven by intense compression, deep burial, and igneous activity.

Migmatite

A composite rock displaying mixed igneous and metamorphic textures formed when high-grade metamorphic rock undergoes partial melting.

Dynamic Metamorphism

Metamorphism along fault zones resulting from intense shearing, producing fine-grained rock with crystal alignment parallel to the fault plane.

Mylonite

A fine-grained metamorphic rock produced by intense shearing and plastic smearing of crystals in fault shear zones during dynamic metamorphism.

Burial Metamorphism

Low-grade metamorphism caused by progressive increases in temperature and pressure beneath sediment accumulations deeper than $8\text{--}15\,\text{km}$ ($T > 320\,^\circ\text{C}$, $3\,\text{kbar}$).

Hydrothermal Metamorphism

Chemical alteration of rock produced when hot, ion-rich fluids (such as heated seawater) circulate through fractured oceanic crust at mid-ocean ridges.

Foliation

A parallel alignment or arrangement of flat or elongated mineral grains in a metamorphic rock, giving it a layered or banded appearance.

Slate

A fine-grained, low-grade foliated metamorphic rock formed from shale, displaying slaty cleavage due to the alignment of microscopic muscovite and chlorite grains.

Phyllite

A foliated metamorphic rock of low-to-intermediate grade where aligned mica grains give the rock surfaces a characteristic silky sheen.

Schist

A medium- to coarse-grained foliated metamorphic rock characterized by prominent, visible platy minerals like muscovite, biotite, chlorite, and talc.

Gneiss

A high-grade metamorphic rock characterized by light silica-rich and dark iron-magnesium-rich mineral bands or layers.

Hornfels

A fine-grained, non-foliated rock created by contact metamorphism of fine-grained parent rocks adjacent to igneous intrusions.

Index Minerals

Specific metamorphic minerals (such as kyanite, sillimanite, and staurolite) that form under distinct temperature and pressure ranges and serve as indicators of metamorphic grade.

Clastic Sediments

Sediment consisting of solid fragments of pre-existing rocks and mineral grains produced by physical weathering.

Grain Roundness

The degree of smoothness of sediment grain corners and edges, ranging from very angular ($R = 0.15$) to well rounded ($R = 0.85$) as transport distance increases.

Lithification

The multi-step process of converting unconsolidated sediment into solid sedimentary rock through compaction and cementation.

Compaction

The reduction of pore spaces between sediment grains caused by the increasing weight of overlying sediments, squeezing out pore fluids.

Cementation

The precipitation of minerals (such as calcite, quartz, or iron oxides) from pore fluids into grain spaces, binding sediment into rock.

Conglomerate

A coarse-grained clastic sedimentary rock composed mostly of rounded gravel fragments larger than $2\,\text{mm}$.

Breccia

A coarse-grained clastic sedimentary rock composed mostly of angular gravel fragments larger than $2\,\text{mm}$.

Arkose

A field-classified sandstone rich in quartz and feldspar grains.

Graywacke

A dark, poorly sorted lithic sandstone containing abundant rock fragments embedded in a matrix of fine-grained clay.

Limestone

A carbonate sedimentary rock composed mostly of the mineral calcite ($\text{CaCO}_3$), primarily produced through biological activity.

Dolostone

A carbonate sedimentary rock composed of the mineral dolomite ($\text{CaMg(CO}_3)_2$), formed by replacement of calcite or precipitation in hypersaline water.

Chert

A hard chemical or biogenic sedimentary rock composed of cryptocrystalline quartz, often originating from microscopic silica-secreting plankton like radiolarians.

Evaporites

Chemical sedimentary rocks (such as gypsum and halite) that precipitate from solution during the evaporation of water.

Graded Bedding

A bedding layer characterized by a progressive upward decrease in grain size, formed by settling from waning sediment-laden currents like turbidites.

Cross-Bedding

Inclined internal layering within larger horizontal sedimentary beds, formed by the migration of wind or water dunes and ripples.

Mudcracks

Polygonal desiccation cracks formed in clay-rich sediment as it dries out upon exposure to air.

Bioturbation

The physical churning, burrowing, and reworking of sedimentary layers by organisms.

Physical Weathering

The mechanical fragmentation of rock into smaller pieces without changing its chemical composition.

Chemical Weathering

The process by which rocks break down through chemical alteration or dissolution from contact with air, water, and acidic solutions.

Hydrolysis

A chemical weathering reaction in which hydrogen ions in acidic water react with minerals, such as feldspar transforming into clay minerals.

Soil Horizon Profile

The vertical arrangement of distinct layers (O, A, E, B, C) developed in soil by chemical weathering, leaching, organic accumulation, and mineral translocation.

Munsell Color System

A system used to systematically describe soil color using three components: Hue, Value (relative darkness), and Chroma (color saturation).

Oxisols (Laterites)

Highly weathered, red or yellow soils rich in iron and aluminum oxides formed in hot, humid tropical environments with high rainfall.

Vertisols

Clay-rich soils characteristic of wet/dry monsoonal climates that expand when wet and contract when dry, forming distinct slickensides and gilgai microrelief.

Aridosols

Soils formed in warm, dry climates with low annual rainfall ($400\text{--}600\,\text{mm}$), characterized by the accumulation of calcium carbonate nodules or calcrete layers.

Histosols

Organic soils (peats) formed in poorly drained, continuously wet environments with thick surface O-horizons.

Pahoehoe Flow

A fluid basaltic lava flow that solidifies into a smooth, ropy, or wrinkled outer surface.

Aa Flow

A viscous basaltic lava flow that solidifies into a rough, jagged, and rubbly surface of broken clinkers.

Pillow Lava

Basaltic lava erupted under water that cools rapidly into stacked, bulbous bodies with glassy crusts.

Volcanic Bomb

A streamlined blob of lava ejected from a volcanic vent that cools and solidifies into shape while flying through the air.

Pyroclastic Flow

A superheated avalanche of gas, ash, and pumice moving rapidly down the flanks of a volcano during explosive eruptions.

Lahar

A destructive volcanic mudflow created when volcanic ash and debris mix with water from rain, snowmelt, or crater lakes.

Shield Volcano

A broad, gently sloped volcano built by low-viscosity basaltic lava flows that pour fluidly from central vents or fissures.

Cinder Cone

A small, steep-sided volcanic cone constructed entirely from ejected basaltic lava fragments (cinders/scoria).

Stratovolcano (Composite Volcano)

A large, steep-sided volcano constructed of alternating layers of lava flows, volcanic ash, and pyroclastic deposits.

Caldera

A large circular or oval volcanic depression formed when the roof of a magma chamber collapses following a major eruption.

Flood Basalts

Vast, thick, flat-lying accumulations of basaltic lava erupted rapidly from fissure vents over enormous geographical regions.

Decompression Melting

Melting of hot mantle rock triggered by a decrease in pressure as it rises toward shallower depths without adding heat.

Flux Melting

Melting triggered when water or other volatiles enter hot mantle rock, lowering its melting temperature at subduction zones.

Bowen's Reaction Series

A systematic model illustrating the sequence in which silicate minerals crystallize from a cooling magma across a spectrum of temperatures.

Fractional Crystallization

The process where early-crystallized minerals are physically separated from magma, causing the remaining liquid to become progressively enriched in silica.

Phaneritic Texture

A coarse-grained igneous texture in which mineral grains are visible to the naked eye, indicating slow subterranean cooling.

Aphanitic Texture

A fine-grained igneous texture in which mineral grains are microscopic, indicating rapid cooling at or near Earth's surface.

Porphyritic Texture

An igneous texture featuring larger crystals (phenocrysts) set within a fine-grained groundmass, indicating a two-stage cooling history.

Dike

A sheet-like tabular igneous intrusion that cuts across surrounding rock layers.

Sill

A sheet-like tabular igneous intrusion injected parallel to pre-existing sedimentary or volcanic rock layers.

Batholith

A large composite mass of intrusive igneous rock formed from multiple plutons with an exposed surface area exceeding $100\,\text{km}^2$.

Xenolith

A foreign piece of country rock incorporated as an inclusion inside an igneous intrusion without completely melting.