Sulfidic metatroctolite from the the Stillwater Mine, Beartooth Mountains, Montana. This Stillwater troctolite has had the oilvine component metamorphosed to black serpentine, while the gray plagioclase feldspar component is preserved.
Troctolite is a coarsely-crystalline, intrusive igneous rock that is composed mostly of olivine and plagioclase feldspar, with minor amounts of other minerals such as pyroxene and chromite. It is typically coarse-grained and has a distinctive greenish-gray color. Troctolite is formed through the solidification of magma deep within Earth's mantle, and is often associated with other ultramafic rocks such as dunite and peridotite. The name "troctolite" comes from the Greek word "troktos," which means twisted or plaited, referring to the twisted appearance of some troctolite rocks.
Troctolite is relatively rare and is not commonly found on Earth's surface, but it is an important rock type for geologists studying the composition and evolution of the Earth's mantle. Troctolite is also found in the lunar highlands.