Geology Terms

On this page you have some basic geology terms.

Alloy A metal that contains more than one kind of metal atoms.

Alteration The changing of mineral composition in a rock.

Banded Iron Formation (BIF) Iron-rich sedimentary layers that consist of alterating red iron-rich chert and grey beds of iron oxide.

Base metals Metals that are mined, but are not considered precious metals, e. g. zinc, lead, copper and tin.

Batholith A huge intrusive igneous rock body which has been formed by the intrusion of many plutons.

Bedrock Rock that is attached to the Earth's crust.

Black smoker The mineral cloud that is formed when hot water sprinkles our of a mid-oceanic ridge.

Buoyancy The upward force that acts on a less dense object which is floating in denser material (e. g. iceberg in the water).

Caldera A depression that forms after an eruption of a volcano when the centre collapses and falls into the magma chamber below.

Cement Mineral material that fills the spaces between grains in a rock.

Chemical weathering The process in which chemical reactions are responsible for changes in mineralisation after the rock comes in contact with air or water.

Cleavage The way a mineral breaks along lines of weakness.

Compositional banding A type of metamorphic foliation with alterating bands of dark and light minerals, which is found in gneiss.

Dike A vertical intrusion that cuts across a rock.      

 dike geology
 Geology terms: A white dike. ©

Ductile deformation The bending of a material, without breaking, when subjected to stress.

Erosion The removal of the surface material of the ground by wind and water.

Fault A fracture where one rock body glides in relation to another.

Felsic A term to desribe igneous rocks which are rich in silica (light in colour as opposed to dark mafic rocks).

Foliation Layering that has been formed by alignment of mineral grains (sedimentary rock) or compositional banding (metamorphic rocks).

Fresh rock Rock that is not altered.

Glass A solid material in which atoms are not arranged in an orderly manner (as opposed to minerals in which they are).

 Geology terms: Foliation. ©

Groundwater Water in the pores of the rock and sediment under the Earth's surface.

Hanging wall The rock above a fault plane.

Landslide A sudden movement of rock down along a non-vertical slope.

Lava Magma that has been brought to the Earth's surface by a volcanic eruption.

Mafic A term to describe igneous rocks that contain predominantly ferromagnetic minerals (they are dark in colour as opposed to felsic igneous rocks).

Magma Molten rock under the surface of the earth.

Meteorite A piece of rock or metal from space that has landed on the Earth (as opposed to comet, which is a piece of space material that orbits the sun but has not landed on the Earth).

Mineral A naturally occuring, solid and homogenous substance with an orderly arrangement of atoms and a definable chemical composition.

 mineral pictures
 Geology terms: Minerals. ©

Ore minerals Minerals that contain enough metal that they are worth mining for economical purposes.

Orogeny A mountain building event.

Outcrop Bedrock that is exposed.

Oxidation The type of chemical weathering in which oxides are formed.

Pluton A large, often round-shaped volcanic intrusion.

Precious metals Metals with high economical value (gold, silver etc)

Quarry A site where rock is extracted from the ground (as opposed to mine where metal is extracted).

 old quarry
 Geology terms: an old quarry. ©

Rain shadow The inland side of a mountain range that doesn't get rain because mountains stop the rain clouds from reaching the area.

Rock A naturally occuring, coherent solid mass that consists of minerals or glass.

Schistocity Foliation that is caused by large, flat mica minerals.

Sediment The loose material on top of the bedrock.

Shield volcano A volcano with a broad dome and non-explosive, mafic lava.

Sill A horizontal volcanic intrusion in the rock.

Soil Sediment that has been affected by surface reactions with rainwater and the addition of organic material.

Stratovolcano A volcano with a tall dome and violently explosive, silica-rich felsic lava. 

Till A glacial deposit consisting of mud, pebbles and rocks. 

Topsoil The top layer of soil, which is commonly dark in colour and rich in nutrients.

Vein Mineral accumulation that is formed by water or other hydrothermal fluids in cracks of rock.

Vesicle The holes in igneous rock (typically basalt) that are formed by air bubbles in lava at the time when the lava cools and turns into rock.

Viscosity A measurement of resistance of material to flow. Viscous lava is cool, silica-rich and contains little volatiles. Non-viscous (low-viscous) lava is hot, mafic and contains many volatiles.

 super volcano
 Geology terms: An erupting volcano. By Storm Crypt via

Volatiles Elements or compounds that evaporate easily (e. g. water and carbon dioxide).

Weathering The breaking up of rock by near-surface chemical or physical processes.

Xenolith An inclusion of a foreign rock in an igneous rock. 

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