Pyroxene is a silicate mineral with the general composition (Mg,Fe)SiO3. Though the basic formula is simple, it is said to be a complex class of minerals. The most common member of the group is augite, which forms dark crystals as a result of the iron and magnesium content. It is said to a ferromagnesian or "mafic" mineral which has a high crystallization temperature and is formed early in the Bowen reaction series.
Lutgens & Tarbuck