Darkly or greenish colored, gabbro is an intrusive rock formed when molten magma becomes trapped in cracks or other layers of rock and gradually cools into a rigid, crystalline mass. The mineral material occurs in large bodies and is common in various locations, such as South Africa, Sudbury, Ontario, Scotland’s Isle of Skye, and the Adirondack Mountains in New York. A relatively dense rock, gabbro is primarily composed of pyroxene and plagioclase feldspar, but olivine, amphibole, and quartz may also be present. Numerous important minerals are also associated with gabbro, and many deposits, such as those found in Lake Superior, have been mined for many years, contributing greatly to local economies in such areas.