Glossary of geological terms

Dyke: A fault or crack in rocks that has later been intruded by other rock types during magmatic activity

Gabbro: A coarse-grained, dark, intrusive, igneous rock

Gneiss: A metamorphic rock, formed from the metamorphosis of granite or sedimentary rock under high temperatures and pressures. It shows distinctive layering of different minerals

Granite: An intrusive, coarse-grained igneous rock, varying from white to pink to grey in colour

Igneous rock: Rocks formed as magma cools below (called plutonic rocks, such as granite) or above (volcanic rocks, such as basalt) the earth’s surface

Intrusive rock: Rock that has been formed as magma crystallises within the crust of the earth

Metamorphic rock: A rock resulting from the transformation of another rock under high heat and pressure conditions

Ophiolite: Part of the earth’s crust and upper mantle that has been uplifted due to tectonic movement and is now exposed above sea-level

Serpentinite: A metamorphic rock, formed by the hydrous (= with water) alteration of igneous rocks such as olivine and pyroxene

Schist: A metamorphic rock, with approximately parallel grains, formed from the metamorphosis of mudstone and shale

Xenolith: A fragment of rock captured and retained within a larger, different rock type as the latter cools and hardens