Glossary of geology

Glossary of Geology

This glossary of geology is a list of definitions of terms and concepts relevant to the field of geology. Geology is the science that studies the Earth's physical structure and substance, its history, and the processes that act on it. This glossary includes terms from various sub-disciplines of geology, such as mineralogy, petrology, paleontology, and seismology.

A

Alluvium

Loose, unconsolidated soil or sediments, which have been eroded, reshaped by water in some form, and redeposited in a non-marine setting.

Anticline

A type of fold that is an arch-like shape and has its oldest beds at its core. Anticlines are typically found in areas of compressional tectonics.

B

Basalt

A common extrusive igneous rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of a planet or moon.

Bedding

The layering that occurs in sedimentary rocks. Each layer is a bed, and the boundary between two beds is a bedding plane.

C

Caldera

A large volcanic crater, typically one formed by a major eruption leading to the collapse of the mouth of the volcano.

Cleavage

The tendency of a mineral to break along flat planar surfaces as determined by the structure of its crystal lattice.

D

Dike

A type of later vertical rock between older layers of rock. Dikes can be either magmatic or sedimentary in origin.

Drumlin

An elongated hill in the shape of an inverted spoon formed by glacial ice acting on underlying unconsolidated till or ground moraine.

E

Erosion

The process by which soil and rock are removed from the Earth's surface by wind, water flow, and other natural processes, and then transported and deposited in other locations.

Extrusive rock

Igneous rock that forms when magma reaches the Earth's surface a volcano and cools quickly.

F

Fault

A fracture or zone of fractures between two blocks of rock, which allows the blocks to move relative to each other.

Fossil

The preserved remains or traces of animals, plants, and other organisms from the remote past.

G

Gneiss

A high-grade metamorphic rock with a banded or foliated appearance, typically composed of alternating darker and lighter colored bands.

Granite

A common type of felsic intrusive igneous rock that is granular and phaneritic in texture.

H

Hydrothermal vent

A fissure on the seafloor from which geothermally heated water issues.

Horst and graben

A geological structure formed by the extension of the Earth's crust, resulting in blocks of crust being uplifted (horst) or down-dropped (graben).

I

Igneous rock

Rock formed through the cooling and solidification of magma or lava.

Intrusive rock

Igneous rock that forms from magma that cools and solidifies within the crust of the planet.

J

Joint

A fracture dividing rock into two sections that have not moved away from each other.

K

Karst

A landscape formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum.

L

Lava

Molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling.

Lithosphere

The rigid outer layer of the Earth, consisting of the crust and upper mantle.

M

Magma

Molten or semi-molten natural material from which all igneous rocks are formed.

Metamorphic rock

Rock that has undergone transformation by heat, pressure, or other natural agencies.

N

Nappe

A large sheetlike body of rock that has been moved far from its original position by faulting or folding.

O

Orogeny

The process of mountain formation, especially by a folding and faulting of the Earth's crust.

P

Plate tectonics

A scientific theory that describes the large-scale motion of Earth's lithosphere.

Pumice

A light, porous volcanic rock that forms during explosive eruptions.

Q

Quartz

A hard, crystalline mineral composed of silicon and oxygen atoms.

R

Rift valley

A linear-shaped lowland between several highlands or mountain ranges created by the action of a geologic rift or fault.

S

Sedimentary rock

Rock that has formed through the deposition and solidification of sediment, especially sediment transported by water, ice, and wind.

Seismology

The scientific study of earthquakes and the propagation of elastic waves through the Earth.

T

Tectonic plate

A massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.

Tuff

A type of rock made of volcanic ash ejected from a vent during a volcanic eruption.

U

Unconformity

A surface of contact between two groups of unconformable strata.

V

Volcano

A rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.

W

Weathering

The breaking down of rocks, soil, and minerals as well as wood and artificial materials through contact with the Earth's atmosphere, waters, and biological organisms.

X

Xenolith

A rock fragment which becomes enveloped in a larger rock during the latter's development and solidification.

Y

Yardang

A streamlined protuberance carved from bedrock or any consolidated or semiconsolidated material by the dual action of wind abrasion by dust and sand and deflation.

Z

Zeolite

A group of silicate minerals with a porous structure that can accommodate a wide variety of cations.