Formula: CaMg [Si₂O₆]      Hardness: 5,5 - 6,5

Diopside is a monoclinic pyroxene mineral.  It forms complete solid solution series with Hedenbergite (FeCaSi
₂O
₆) and Augite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class. Diopside is found in ultramafic (Kimberlite and Peridotite) igneous rocks, and Diopside-rich Augite is common in mafic rocks, such as Olivine Basalt and Andesite. Diopside is also found in a variety of metamorphic rocks, such as in contact metamorphosed skarns developed from high silica Dolomites. It is an important mineral in the Earth's mantle and is common in Peridotite Xenoliths erupted in Kimberlite and Alkali Basalt.

Diopside derives its name from the Greek dis, "twice", and òpsè, "face" in reference to the two ways of orienting the vertical prism. IT was discovered and first described about 1800, by Brazilian naturalist Jose Bonifacio de Andrada e Silva.