Diopside << dy OP syd >> is a widely occurring mineral with a glassy luster. Diopside is sometimes used as a gemstone. It belongs to a group of rock-forming minerals called pyroxenes. Diopside is a silicate rich in calcium and magnesium (see Silicate). Pure diopside is white, and it melts at 1391 °C. The additions of iron and chrome typically make the mineral light green. Metamorphic diopside forms when intense heat and pressure are applied to limestone that consists chiefly of dolomite with silica impurities (see Metamorphism). Igneous diopside also forms during the crystallization of certain kinds of magma (molten rock material) (see Igneous rock).
