Pyroxene crystal. Close-up of a thin section through a pyroxene crystal (orange) in an extrusive igneous rock. The pyroxene crystal is typical for orthorhombic varieties of pyroxene. The pyroxenes are an important group of rock-forming silicate minerals. They are inosilicates (chain silicates), comprised of interlocking chains of silicate tetrahedra (SiO4) with silicon and oxygen in a 1:3 ratio). Magnification: x4.8 when printed 10 centimetres wide.