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Chemical composition CaMg(SiO3)2

Calcium magnesium sillcate

Crystal system Monoclinic
Habit Prismatic, waterworn pebbles
Cleavage Distinct
Fracture Conchoidal
Hardness 5
Optic nature Biaxial +
Refractive index 1.67-1.70
Birefringence 0.025
Dispersion Low, 0.013
Specific gravity 3.3
Lustre Vitreous
Pleochroism Weak to moderate
Star Diopside
Photo courtesy of
Wild Fish Gems

Diopside is a calcium magnesium silicate that crystallizes from magmas. It is usually a fairly uninteresting component of igneous rocks, but there are a few varieties that have gemological merit. The first is a chatoyant (cat's-eye effect) variety. Occasionally, stones have been found that are chatoyant in two directions forming a four pointed star. Ancient civilizations believed that star stones housed living spirits who were looking at you through those stars. One of the most popular varieties of diopside are chrome bearing stones which are vibrant green and transparent. These are found in Russia and East Africa. There is another variety, termed violane, that is bluish violet, used for beads and inlay work.

Diopside forms an isomorphous series with hedenbergite ( CaFe(SiO3)2 ) and the iron that comes from hedenbergite is the prime cause of color in diopside.