ESC1000 Chapter 3 Rocks: Materials of the Solid Earth

Andesite

A gray, fine-grained igneous rock, primarily of volcanic origin and commonly exhibiting a porphyritic texture

Andesitic composition

A compositional group of igneous rocks that contains at least 25 percent dark silicate minerals. The other dominant mineral is plagioclase feldspar. Also called intermediate composition

Basalt

A fine-grained igneous rock of mafic composition

Basaltic composition

A compositional group of igneous rocks indicating that the rock contains substantial dark silicate minerals and calcium-rich plagioclase feldspar. Also called mafic composition

Beds

Parallel layers of sedimentary rock. Also called strata

Biochemical sedimentary rock

Sediment that forms when material dissolved in water is precipitated by water-dwelling organisms. Shells are common examples

Bowen's reaction series

A concept proposed by N. L. Bowen that illustrates the relationships between magma and the minerals crystallizing from it during the formation of igneous rocks

Breccia

A sedimentary rock composed of angular fragments that were lithified

Building material

A category of nonsilicate mineral resource used in building

Cap rock

A necessary part of an oil trap which is impermeable and hence keeps upwardly mobile oil and gas from escaping at the surface

Cementation

One way in which sedimentary rocks are lithified. As material precipitates from water that percolates through the sediment, open spaces are filled, and particles are joined into a solid mass

Chemical sedimentary rock

Sedimentary rock consisting of material that was precipitated from water by either inorganic or organic means

Coal

A sedimentary rock consisting primarily of organic matter, formed in stages from accumulations of large quantities of undecayed plant material. It is used as a fossil fuel

Coarse-grained texture

An igneous rock texture in which the crystals are roughly equal in size and large enough that individual minerals can be identified with the unaided eye

Compaction

A type of lithification in which the weight of overlying material compresses more deeply buried sediment. It is most important in fine-grained sedimentary rocks such as shale

Confining pressure

Stress that is applied uniformly in all directions

Conglomerate

A sedimentary rock composed of rounded, gravel-size particles

Contact metamorphism

Changes in rock caused by the heat from a nearby magma body

Coquina

A coarse rock composed of loosely cemented shells and shell fragments

Crystal settling

During the crystallization of magma, the settling of the earlier-formed minerals that are denser than the liquid portion to the bottom of the magma chamber

Detrital sedimentary rock

Rock formed from the accumulation of material that originated and was transported in the form of solid particles derived from both mechanical and chemical weathering

Differential stress

Forces that are unequal in different directions

Diorite

A coarse-grained intrusive igneous rock primarily composed of plagioclase feldspar and amphibole minerals

Disseminated deposit

Any economic mineral deposit in which the desired mineral occurs as scattered particles in the rock but in sufficient quantity to make the deposit an ore

Evaporite deposits

A sedimentary rock formed of material deposited from solution by evaporation of water.

Extrusive rock

Igneous rock formed when magma solidifies at Earth's surface. Also called volcanic rock

Felsic composition

A compositional group of igneous rocks that indicates a rock is composed almost entirely of light-colored silicates. Also called granitic composition.

Fine-grained texture

A texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished with the unaided eye.

Foliation

A texture of metamorphic rocks that gives the rock a layered appearance

Fossil

The remains or traces of organisms preserved from the geologic past

Fossil fuel

A general term for any hydrocarbon that may be used as a fuel, including coal, oil, natural gas, bitumen from tar sands, and shale oil

Fragmental texture

An igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent volcanic eruption. Also called pyroclastic texture

Gabbro

A dark-green to black intrusive igneous rock composed of dark silicate minerals. Gabbro makes up a significant percentage of oceanic crust

Glassy texture

A term used to describe the texture of certain igneous rocks, such as obsidian, that contain no crystals.

Gneiss

Medium- to coarse-grained banded metamorphic rocks in which granular and elongated minerals dominate

Granite

An abundant, coarse-grained igneous rock, composed of about 10 to 20 percent quartz and 50 percent potassium feldspar. Granite is used as a building material

Granitic composition

A compositional group of igneous rocks that indicates a rock is composed almost entirely of light-colored silicates. Also called felsic composition

Groundmass

The matrix of smaller crystals within an igneous rock that has porphyritic texture

Hydraulic fracturing

A method of opening up pore space in otherwise impermeable rocks, permitting natural gas to flow out into wells

Igneous rock

A rock formed by the crystallization of molten magma

Industrial mineral

A nonmetallic mineral resource that is used in industry

Intermediate composition

A compositional group of igneous rocks that contains at least 25 percent dark silicate minerals. The other dominant mineral is plagioclase feldspar. Also called andesitic composition

Intrusive rock

Igneous rock that formed below Earth's surface. Also called plutonic rock

Lava

Magma that reaches Earth's surface

Limestone

A chemical sedimentary rock composed chiefly of calcite. Limestone can form by inorganic means or from biochemical processes

Lithification

The process, generally cementation and/or compaction, of converting sediments to solid rock.

Mafic composition

A compositional group of igneous rocks indicating that the rock contains substantial dark silicate minerals and calcium-rich plagioclase feldspar. Also called basaltic composition

Magma

A body of molten rock found at depth, including any dissolved gases and crystals

Magmatic differentiation

The process of generating more than one rock type from a single magma

Metamorphic rock

Rocks formed by the alteration of preexisting rock deep within Earth (but still in the solid state) by heat, pressure, and/or chemically active fluids

Metamorphism

The changes in mineral composition and texture of a rock subjected to high temperature and pressure within Earth

Nonfoliated

Describes metamorphic rocks that do not exhibit foliation

Nonmetallic mineral resource

A mineral resource that is not a fuel and is not processed for the metals it contains

Obsidian

A volcanic glass of felsic composition

Oil trap

A geologic structure that allows for significant amounts of oil and gas to accumulate

Pegmatite

A very coarse-grained igneous rock (typically granite) commonly found as a dike associated with a large mass of plutonic rock that has smaller crystals. Crystallization in a water-rich environment is believed to be responsible for the very large crystals

Peridotite

An igneous rock of ultramafic composition thought to be abundant in the upper mantle

Phenocryst

In an igneous rock with a porphyritic texture, a conspicuously large crystal embedded in a matrix of finer-grained crystals called the groundmass

Phyllite

A metamorphic rock composed mainly of fine crystals of muscovite, chlorite, or both

Plutonic rock

Igneous rock that formed below Earth's surface. Also called intrusive rock

Porphyritic texture

An igneous texture consisting of large crystals embedded in a matrix of much smaller crystals

Pumice

A light-colored, glassy vesicular rock commonly having a granitic composition

Pyroclastic texture

An igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent volcanic eruption. Also called fragmental texture

Quartzite

A hard, nonfoliated metamorphic rock formed from quartz sandstone

Regional metamorphism

Metamorphism associated with large-scale mountain-building processes

Reservoir rock

The porous, permeable portion of an oil trap that yields oil and gas

Rhyolite

The fine-grained equivalent of the igneous rock granite, composed primarily of light-colored silicates

Rock cycle

A model that illustrates the origin of the three basic rock types and the interrelatedness of Earth materials and processes

Sandstone

An abundant, durable detrital sedimentary rock primarily composed of sand-size grains.

Schist

Medium- to coarse-grained metamorphic rocks having a foliated texture, in which platy minerals dominate

Sediment

Unconsolidated particles created by the weathering and erosion of rock, by chemical precipitation from solution in water, or from the secretions of organisms and transported by water, wind, or glaciers

Sedimentary rock

Rock formed from the weathered products of preexisting rocks that have been transported, deposited, and lithified.

Shale

The most common sedimentary rock, consisting of silt- and clay-size particles

Siltstone

A fine-grained sedimentary rock composed of silt-sized grains intermixed with clay-sized sediment.

Slate

A very fine-grained metamorphic rock containing platy minerals and having excellent rock cleavage

Source rock

The sedimentary rocks in which petroleum and natural gas originate

Strata

Parallel layers of sedimentary rock. Also called beds.

Texture

The size, shape, and distribution of the particles that collectively constitute a rock

Travertine

A form of limestone (CaCO3) that is deposited by hot springs or as a cave deposit.

Ultramafic

Refers to igneous rocks composed mainly of iron- and magnesium-rich minerals

Vein deposit

A mineral filling a fracture or fault in a host rock. Such deposits have a sheetlike, or tabular, form.

Vesicular texture

A term applied to igneous rocks that contain small cavities called vesicles, which are formed when gases escape from lava

Volcanic rock

Igneous rock formed when magma solidifies at Earth's surface. Also called extrusive rock

The surface process that slowly disintegrates and decomposes rock is called __________.

weathering

The process that results as the random movement of ions slows and the ions come to rest organized within a pattern is called __________.

crystallization

Igneous rocks showing voids left by escaping gas bubbles are also called __________.

extrusive

Which of the following characteristics is shown by obsidian?

Glassy texture

Which of the following terms is not used as one of the four basic igneous rock textures?

Felsic

Rocks with abundant dark-colored silicate minerals containing iron and magnesium such as olivine and pyroxene are best described as "__________."

mafic

Rhyolite has the same chemical composition as _________.

granite

Detrital sedimentary rocks are subdivided according to __________.

particle size

Which of the following cannot be an example of biochemical sedimentary rock?

Sandstone

Which of the following is not a chemical sedimentary rock?

Shale

Which of the following is considered a nonfoliated metamorphic rock?

Marble

Which one of the following is an industrial mineral resource?

Rock gypsum

Important metallic minerals, such as gold and copper, are sometime distributed in trace amounts throughout the whole rock in a ____________deposit.

disseminated