Diopside

Crystals of diopside may be colourless, but are more usually bottle-green, brownish green or light green. The more iron-rich and magnesium-poor they are, the darker the color - almost to black. Very bright green diopside, coloured by chromium, is called chrome diopside. Violet blue crystals, coloured by manganese, have been discovered in Italy and United States, and are known as violane. It is polished as beads when massive; cut for collectors when transparent; and cut in cabochon when fibrous.

Gem-quality chrome diopside can be found in Burma, Siberia (Russia), Pakistan, and South Africa. Other diopside localities include Austria, Brazil, Italy, United States, Madagascar, Canada and Sri Lanka. Dark green to black diopside, which shows a 4-rayed star when cut in cabochon, has been found in southern India since 1964.

Diopside Pictures

Rough diopside

Diopside Properties

Chemical Composition: 
Silicate of calcium and magnesium (pyroxene mineral) - CaMgSi2O6 + Fe, Mn, Cr.
Classification / Type: 
Diopside belongs to the diopside - hedenbergite isomorphous series where there is a total replacement of magnesium by iron. Gives rise to a variation in properties, with higher values for stones with higher iron content.
Colors / Varieties: 
  • Green (light-dark-bright shades), blackish green, yellow / reddish brown, black, colorless.
  • Chrome diopside: bright green (greater Cr %)
  • Violane: dark violet blue.
  • Cat's eye and 4-rayed star (commonly black)
Crystal System / Forms: 
Monoclinic System / Prismatic well formed crystals also tabular, massive.
Hardness: 
5.5
Specific Gravity: 
3.22 - 3.38 (higher with Fe %)
Cleavage / Fracture: 
Perfect 2 directional prismatic cleavage / Conchoidal fracture
Optic Character: 
Anisotropic, D.R.; Biaxial positive
Lustre: 
Vitreous
Refractive Index / Birefringence: 
1.675 - 1.701 / 0.026; Range: 1.655 - 1.730
Pleochroism: 
Weak: green / brownish green / brown
Magnification: 
Short needle like inclusions, metallic appearing inclusions, fan shaped fingerprints, doubling.
U.V. Fluorescence: 
Variable
Spectrum: 
  • Diopside: Lines at 505nm, 493nm, 446nm
  • Chrome Diopside: Lines at 508nm, 505nm, bands at 635nm, 655nm, 670nm, doublet at 690nm.
Cause of Color: 
  • Iron / Chromium: Green
  • Manganese: Violane
Specific Tests: 
Star diopside is attracted to a magnet since they contain magnetite needles.
Simulants (with separation tests): 
Enstatite (R.I., birefringence), Peridot (R.I., spectrum), Kornerupine (R.I., birefringence, spectrum, pleochroism), Tourmaline (optic figure, R.I., birefringence, S.G.), Moldavite (optic character)
Geological Occurrence: 
In calcium rich metamorphic rocks and kimberlites.
Sources: 
Burma, Russia, Sri Lanka, India, Madagascar, U.S.A. (California), Kenya, etc.