A large, geologically significant group of dark, rock-forming silicate minerals. Pyroxene is found in abundance in a wide variety of igneous and metamorphic rocks. Because of their structural complexity and their diversity of chemical composition and geologic occurrence, these minerals have been intensively studied by using a wide variety of modern analytical techniques. Knowledge of pyroxene compositions, crystal structures, phase relations, and detailed microstructures provides important information about the origin and thermal history of rocks in which they occur.