Diopsid

Diopsid, also known as diopside, is a monoclinic pyroxene mineral with the chemical formula CaMgSi2O6. It forms part of the diopside-hedenbergite solid solution series, with hedenbergite CaFeSi2O6 representing the iron-rich end member. Diopsid occurs in high-temperature, calcium-rich metamorphic environments and in certain igneous rocks, including calc-silicate rocks, skarns, and dioritic to gabbroic intrusions.

Crystals of diopsid are typically elongated and prismatic, sometimes tabular, with a vitreous luster and a pale streak. The color ranges from colorless to greenish gray, while chromium-bearing varieties exhibit a vivid green hue. Cleavage occurs in two directions at near 90 degrees (approximately 87° and 93°). The hardness on the Mohs scale is about 5.5–6, and the specific gravity is around 3.2–3.5. Diopside ranges from translucent to opaque in many specimens.

Occurrence and geology: diopsid is found worldwide and is common in contact metamorphic rocks, such as skarns formed from limestone or dolostone adjacent to igneous intrusions, as well as in marbles. It also occurs in mafic and ultramafic igneous rocks and can be present as inclusions in metamorphic rocks. Associated minerals often include calcite, wollastonite, tremolite, garnet, and feldspars.

Applications: gem varieties include chrome diopside, a chromium-rich green gemstone valued in jewelry; jade diopside is a marketed term for green diopside used in lapidary. Aside from gems, diopside is mined as a minor source of calcium and magnesium but has limited industrial use.