Interlude A, B, C and Chapter 4

Rock

A naturally occurring solid consisting of minerals or glass.

Cement

Material that holds together individual grains in some rocks.

Interlocking crystals

Crystals that fit together to hold a rock together.

Igneous rock

Rock formed by the cooling and solidification of molten rock.

Sedimentary rock

Rock formed when sediments are cemented together.

Metamorphic rock

Rock formed when existing rock is changed by heat and/or pressure.

Rock cycle

The transformation of Earth materials from one rock type to another over time.

Sediment

Material formed from the weathering of preexisting rocks.

Weathering

The breakdown and alteration of solid rock into sediment.

Erosion

The transport of weathered material from one place to another.

Magma

Molten rock below Earth's surface.

Lava

Molten rock at or on Earth's surface.

Crystallization

The cooling of magma that results in atoms bonding and minerals forming.

Preexisting rock

An existing igneous, sedimentary, or metamorphic rock that can be transformed.

Heat and pressure

Conditions that can transform existing rock into metamorphic rock.

Continental collision

A tectonic setting where sedimentary rocks can undergo metamorphism.

Continental rifting

A setting where metamorphic rocks can melt and form igneous rocks.

Rock aggregate

A coherent mass made of one or more minerals or glass.

Rock layers

Layers in which sedimentary rocks commonly accumulate at Earth's surface.

Rock transformation

The changing of one rock type into another through rock-cycle processes.

Physical weathering

The breaking of intact rock into smaller grains or chunks.

Chemical weathering

Chemical reactions that alter or destroy minerals.

Frost wedging

Water freezes in rock cracks, expands, and enlarges them.

Salt wedging

Salt crystals precipitate as water evaporates, enlarging rock crevices.

Thermal expansion

Heating expands outer rock layers, while cooling contracts them.

Root wedging

Growing plant roots widen fractures in rocks.

Animal attack

Physical weathering caused by animals or human activity.

Mechanical weathering

The physical breakdown of rock into smaller pieces.

Dissolution

The dissolving of minerals in water or weak acid.

Oxidation

Oxygen reacts with elements to form oxides, such as rust.

Hydrolysis

Water ions react with minerals to form new compounds, often clay minerals.

Hydration

Water is absorbed into mineral crystal structures, causing swelling.

Carbonic acid

A weak acid produced when carbon dioxide dissolves in water.

Halite

A mineral that is highly soluble in water.

Iron oxide

A compound formed when oxygen reacts with iron, commonly called rust.

Weathering agent

A factor such as water that contributes to the breakdown or alteration of rock.

Surface area

The exposed area of rock available for chemical weathering reactions.

Differential weathering

Uneven weathering caused by differences in rock properties and climate.

Climate

Temperature and precipitation conditions that influence weathering rates.

Freeze-thaw

Repeated freezing and thawing of water that can contribute to frost wedging.

Intrusive igneous rock

Igneous rock that crystallizes below Earth's surface.

Extrusive igneous rock

Igneous rock that crystallizes at or on Earth's surface.

Volatiles

Dissolved gases in molten rock, such as water vapor and carbon dioxide.

Silicate tetrahedron

A structural unit formed by silicon and oxygen atoms during crystallization.

Aphanitic texture

Fine-crystalline texture with crystals too small to see with the naked eye.

Extrusive

Phaneritic texture

Coarse-crystalline texture with visible crystals.

Extrusive

Porphyritic texture

Texture with large crystals embedded in a matrix of smaller crystals.

Intrusive followed by extrusive

Phenocrysts

Large crystals within a porphyritic rock.

Groundmass

The smaller-crystal matrix surrounding phenocrysts.

Vesicular texture

Texture with holes left by escaping gas bubbles.

Extrusive

Glassy texture

Texture formed by very rapid cooling that prevents orderly crystal formation.

Pyroclastic texture

Texture formed from consolidated fragments ejected during explosive eruptions.

Pegmatitic texture

Exceptionally coarse-crystalline texture formed during late-stage crystallization of magma.

Intrusive

Felsic composition

Composition dominated by light silicate minerals, common in continental crust.

Intermediate composition

Composition with mostly light silicates and up to 50% dark silicates.

Mafic composition

Composition dominated by dark silicates, common in oceanic crust.

Ultramafic composition

Composition made almost entirely of dark silicate minerals, common in the upper mantle.

Granite

Felsic, intrusive igneous rock with phaneritic texture.

Basalt

Mafic, extrusive igneous rock with aphanitic texture.

Gabbro

Mafic, intrusive igneous rock with phaneritic texture.