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Geosciences LibreTexts

16.09: Diopside

  • Page ID
    4138
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    Diopside
    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

    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 is 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.