Gabbro specimen; Rock Creek Canyon, eastern Sierra Nevada, California.

A thin section of gabbro under the microscope shows the crystals of which it is made.

A gabbro landscape on the main ridge of the Cuillin, Isle of Skye, Scotland.

Gabbro as a xenolith ('foreign' rock) in a granite, Sierra Nevada, Rock Creek Canyon, California.

Gabbro is a large group of dark, coarse-grained, igneous rocks. They are chemically equivalent to basalt. The rocks are plutonic, formed when molten magma is trapped under the Earth's surface and cools into a crystalline mass.

Most of the Earth's surface has gabbro in the oceanic crust, produced by basalt magmatism at mid-ocean ridges. In general, when the gabbro is formed, it lies above the Earth's mantle, and below the basalt.