Diopside

Crystals of diopside might be colourless but tend to be more usually bottle-green, brownish green or light green. The greater iron-rich and magnesium-poor they're, 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 the United States, and could be called violane. It's polished as beads when massive; cut for collectors when transparent; and cut en 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, the united states, Madagascar, Canada and Sri Lanka. Green to black diopside, which shows a 4-rayed star when cut in cabochon, has been discovered in southern India since 1964.

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

Dispersion: 

-

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

Treatment (Enhancement): 

-

Specific Tests & Remarks: 

Star diopside is attracted to a magnet since they contain magnetite needles.

Synthesis: 

-

Simulants (with key 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.

Cuts & Uses: 

Facetted cuts and cabochon.