Diopside is a monoclinic pyroxene mineral with composition MgCaSi₂O₆. It forms solid solution series with hedenbergite (FeCaSi₂O₆) and augite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class. It has two distinct prismatic cleavages at 87 and 93° typical of the pyroxene series. It has a Mohs hardness of six and a specific gravity of 3.25 to 3.55. It is transparent to translucent with indices of refraction of nα=1.663 - 1.699, nβ=1.671 - 1.705 and nγ=1.693 - 1.728. The optic angle is 58° to 63°.

Diopside is found in mafic (olivine basalts and andesites) to ultramafic (kimberlite and peridotite) igneous rocks. It is also found in a variety of metamorphic rocks. It often occurs in contact metamorphosed skarns developed from high silica dolomites. It is also a constituent of the Earth's mantle.

Gemstone quality diopside is found in two forms: the black star diopside and the chrome diopside (which includes chromium giving it a rich green colour). At 5.5-6.5 on the Mohs scale, chrome diopside is relatively soft to scratch. Mohs scale of hardness does not measure tensile strength or resistance to fracture.

Chrome diopside ((Ca,Cr)(Mg,Fe)Si₂O₆) is found near kimberlite pipes, and as such is a prospecting indicator for diamonds. Occurrences are reported in Canada, South Africa, Russia and a wide variety of other locations.

Diopside was first described about 1800 and derives its name from the Greek dis - "two kinds" or "double" and opsis - "opinion" or "appearance" in reference to the two ways of orienting the vertical prism.

References

• Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., Wiley, pp 403-404, ISBN 0471805807
• Diopside - Mindat
• Chromian diopside - Mindat with localities
• Webmineral
• Mineral galleries
• Handbook of Mineralogy, Mineral Data Publishing, 2001, Diopside PDF version

Magnesium minerals | Calcium minerals | Silicate minerals

Diopsid | Diopsido | Diopside | Diopszid | Diopsiet | Diopsyd | Diópsido