Gabbro

Gabbro is a dark, medium- to coarse-grained intrusive igneous rock composed of calcium plagioclase, pyroxene, and minor olivine, but no quartz. It is the intrusive equivalent of a basalt. Gabbros are often used as facing stones on buildings, especially the attractive dark varieties, but it is too fragile to make a good construction material. Colour: dark grey, greenish, brownish.

Mineralogy: essential plagioclase and pyroxene, other minerals include olivine, hornblende, spinel, ilmenite, magnetite, apatite.

Classification: basic plutonic igneous rock.

Occurrence: deeper continental crust, widespread.

Texture: course grained, granitic texture, crystals intergrown; may have lath like crystals of feldspar aligned parallel to layering.

Structure: commonly layered, may show alternating light (feldspar rich) and dark (pyroxene and/or olivine) layers.