Silicate of calcium and magnesium. of the monoclinic pyroxene group. The name is derived from the Greek dis and opsis, meaning "double vision,” because it is clearly birefringent. Some of the magnesium may be replaced by iron.

Crystal system Morioclinic.
Appearance Diopside occurs in somewhat stocky or elongated prismatic crystals, or as aggregates of rod shaped crystals, the color often being bottle green to blackish green, but also bright green or dull yellowish green. In some cases it is semiopaque. with internal fibrosity. The fairly transparent types are used as gems, as are the semiopaoue specimens that exhibit chatoyancy or asterism if appropriately cut.

Physical properties it has a hardness of 5.5-6, therefore not very high. The density varies from 3.27 to 3.31g/cm“, increasing with the iron content. The refractive indices are about mt 1.671—1.602, ny 1.699—1.7'26, so there is a very marked birefringence of 0.028—0.024.

Genesis Diopside is common in contact metamorphosed limestones or serpentinous rocks and the kimberlites of South Africa.

Occurrence It is fairly widespread; found mainly in South Africa, Burma, Sri Lanka, Madagascar, and Brazil, but also Italy (Val d'Ala). Austria (Tyrol), Finland. and the United States. it is occasionally found in metamorphosed blocks of limestone ejected by Vesuvius.
The transparent, greenish varieties are used as gems and have no separate name; however, the brilliant green variety, which also contains chrome {as can be seen, for example, trom the absorption spectrum}, is known as chrome diopside.

Appearance Gem diopside is generally a dark, bottle green- but may also be light. rather dull, yellowish green. However, when the color is due to chrome, it can be a livelier, almost emerald hue. It has unexceptional, vitreous luster, and is given both mixed, oval, and cabochon cuts. It is not very common, and gems weighing many carats are rare.

Distinctive features The bottle green color with quite strong birefringence is fairly characteristic, but as it can closely resemble certain tourmalines and olivines of a similar color. the Physical Properties normally have to be measured to confirm identification.

Occurrence Gem diopside comes mainly from Brazil, SriLanka, Burma. and Madagascar. New York, ltalv, Austria. and Switzerland also produce fine quality gemstones. Chrome diopside is found in South Africa and Finland.

Value It is not a very well known gem. outside the areas where it is mined and cut, and is not highly prized. The brilliant green (chrome diopside) varieties are of low value.

even compared with other secondary gems. The dark or light green varieties are worth still less.

Simulants and synthetics It is neither imitated nor produced synthetically.