Cameroon GCE O-Level Geology key terms

A naturally occurring, inorganic solid with a definite chemical composition and an ordered internal atomic structure. Minerals are the building blocks of rocks and are identified by properties such as hardness, cleavage and colour.

A naturally formed aggregate of one or more minerals, or of solid organic or glassy material. Rocks are grouped as igneous, sedimentary or metamorphic according to how they formed.

Rock formed when molten material (magma or lava) cools and solidifies. Slow cooling underground gives coarse crystals, while rapid cooling at the surface gives fine crystals or glass.

Molten rock material generated beneath the Earth's surface, containing dissolved gases and often crystals. When it reaches the surface it is called lava and cools much faster.

Molten rock that has erupted onto the Earth's surface. Because it cools quickly in air or water, lava usually forms fine-grained or glassy rock rather than large crystals.

Igneous rock that solidified from magma below the surface. Insulation by surrounding rock slows cooling, so crystals grow large and the rock is coarse-grained, for example granite.

Igneous rock formed from lava that cooled at or near the surface. Rapid cooling produces fine-grained or glassy textures, as in basalt and obsidian.

Rock formed at or near the surface from deposited sediment that is later compacted and cemented, or from chemical precipitation. Layers called beds are typical, and fossils may be preserved.

Rock changed in the solid state by heat, pressure or chemically active fluids, usually deep in the crust. New minerals and layering develop, as in slate from shale or marble from limestone.

The breakdown of rocks in place by physical, chemical or biological processes. The broken material stays where it forms, unlike erosion, which removes and transports it.

The removal and transport of weathered rock material by agents such as running water, wind, ice or gravity. Erosion shapes valleys and carries sediment to depositional sites.

The laying down of transported sediment when the carrying agent loses energy, for example where a river slows or a glacier melts. Deposited material may later become sedimentary rock.

The squeezing of sediment under the weight of overlying layers, which reduces pore space and expels water. Together with cementation it turns loose sediment into solid sedimentary rock.

The binding of compacted sediment grains by minerals precipitated from pore water, such as calcite, silica or iron oxide. This process hardens sediment into sedimentary rock.

The arrangement of sedimentary rock in layers or beds, each representing a period of deposition. Differences in grain size or colour make the layers visible in cliffs and road cuts.

The preserved remains or trace of an organism older than about ten thousand years, found mainly in sedimentary rocks. Fossils help date rocks and reveal past environments.

A ranking of ten reference minerals from talc (1) to diamond (10) used to compare hardness. A mineral scratches those below it and is scratched by those above it.

The tendency of a mineral to break along flat planes that follow weak zones in its atomic structure. Mica shows one perfect cleavage, while quartz shows none.

The colour of the powder left when a mineral is rubbed on unglazed porcelain. Streak is often more reliable than the mineral's surface colour for identification.

The theory that the lithosphere is divided into rigid plates that move over the weaker asthenosphere. Their interactions cause earthquakes, volcanoes, mountain building and ocean formation.

A plate margin where two plates move towards each other. One may subduct beneath the other, producing deep-sea trenches, volcanic arcs, fold mountains and powerful earthquakes.

A plate margin where two plates move apart and new crust forms from rising magma. Mid-ocean ridges and rift valleys are typical features, with shallow earthquakes and basaltic volcanism.

The sinking of a denser oceanic plate beneath a lighter plate at a convergent margin. It generates deep earthquakes, magma that feeds volcanoes, and a deep ocean trench.

A sudden release of stored elastic energy in the crust, producing seismic waves that shake the ground. The point of origin underground is the focus, and the point above it is the epicentre.

An instrument that records ground motion during an earthquake as a trace called a seismogram. Arrival times of P and S waves help locate the focus and estimate the earthquake's strength.

A vent or opening in the crust through which magma, gases and ash escape to the surface, often building a cone. Volcanoes cluster along plate margins and over hot spots.

A fracture in rock along which the two sides have moved relative to each other. Sudden slip on a fault causes earthquakes, and movement may be vertical, horizontal or oblique.

A bend in layered rock produced by compressional forces, with an arch-shaped anticline and a trough-shaped syncline. Folds are common in mountain belts such as the Alps.

A mountain range formed where thick layers of rock are compressed and buckled into folds, usually at a convergent plate margin. The Himalayas and the Alps are examples.

A vertical section through soil from the surface down to the underlying rock, showing distinct layers called horizons. Topsoil, subsoil and weathered parent material are usually visible.

The loose surface layer of weathered mineral particles mixed with organic matter, water and air, in which plants grow. Its character depends on parent rock, climate and time.

Water held in the pore spaces and cracks of rock and soil below the water table. It supplies wells and springs and can dissolve limestone to form caves.

A rock or sediment layer that stores and transmits enough groundwater to supply a well or spring. Sandstone and fractured limestone make good aquifers; clay does not.

The ability of a rock or soil to allow fluids to pass through its connected pore spaces and cracks. High permeability aids drainage and groundwater flow; clay has very low permeability.

The proportion of a rock's volume made up of pore spaces, expressed as a percentage. High porosity does not guarantee that water can flow if the pores are not connected.

The upper surface of the saturated zone below ground, where pore spaces are completely filled with water. It rises in wet seasons and falls in dry ones, following the land surface roughly.

A concentration of a valuable mineral or metal that can be mined at a profit. Whether a deposit is economic depends on grade, size, accessibility and the market price.

A rock or mineral body from which a metal or other valuable substance can be extracted profitably. Common ore minerals include galena for lead and cassiterite for tin.