Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Diopside is a monoclinic pyroxene mineral with composition MgCaSi2O6. It forms complete solid solution series with hedenbergite and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class. It has two distinct prismatic cleavages at 87 and 93Â° typical of the pyroxene series. It has a Mohs hardness of six, a Vickers hardness of 7.7 GPa at a load of 0.98 N, and a specific gravity of 3.25 to 3.55. It is transparent to translucent with indices of refraction of nÎ±=1.663â€“1.699, nÎ²=1.671â€“1.705, and nÎ³=1.693â€“1.728. The optic angle is 58Â° to 63Â°. Diopside is found in ultramafic 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.