Rock Group

Igneous (Mafic)

Grain Size

Minerals grains are coarse and roughly equal in size. This texture is also described as phaneritic, meaning “visible”, referring to the grains.

Composition

Gabbro is largely composed of pyroxene (the dark mineral) and plagioclase (the white mineral).

Key Features

Gabbro is the plutonic equivalent of basalt, meaning that it has the same composition as basalt, but instead of cooling quickly on the surface and therefore only growing small, aphanitic mineral crystals, gabbro cools more slowly deeper in the Earth, giving minerals more time to grow into a phaneritic texture.