Dioptase

Dioptase is really a beautiful, vivid emerald-green, having a hint of blue. It's high fire, but this really is masked by its strong colour, which could make stones translucent than transparent. Prized through the collector because of its colour, it's nonetheless rarely faceted, as stones are brittle and fragile, and too soft to become worn. It may also be wrongly identified as emerald.
The highest quality crystals are present in copper deposits in Russia, Namibia, Zaire, Chile, and Arizona (USA).

Properties

Chemical Composition: 

Copper Silicate - CuSiO₂(OH)₂

Classification / Type: 

-

Colors / Varieties: 

Emerald green, bluish green (over saturated color)

Crystal System / Forms: 

Trigonal System / Prismatic crystals.

Hardness: 

5

Specific Gravity: 

3.28 - 3.35

Cleavage / Fracture: 

Perfect 3 directional cleavage / Conchoidal fracture

Optic Character: 

Anisotropic, D.R.; Uniaxial positive.

Lustre: 

Vitreous.

Refractive Index / Birefringence: 

1.644 - 1.697 / 0.053; Range: 1.633 - 1.710<

Pleochroism: 

Weak

Dispersion: 

0.036

Magnification: 

3 directional cleavage cracks, doubling.

U.V. Fluorescence: 

Inert.

Spectrum: 

Copper

Cause of Color: 

Broad band centered at 550nm and strong absorption in the blue and violet region.

Treatment (Enhancement): 

-

Specific Tests & Remarks: 

• Very intense green
• Strong doubling
• Attacked by acids

Synthesis: 

-

Simulants (with key separation tests): 

• Natural / synthetic emerald (R.I., birefringence, S.G.), Peridot (inclusions, spectrum), Diopside (R.I., birefringence)

Geological Occurrence: 

In the oxidized zones of copper deposits. Clean specimens are generally in sizes below 1.5 carat.

Sources: 

Russia, Zaire, Chile, Namibia, U.S.A.

Cuts & Uses: 

Facetted, cabochon cut, sometimes as beads for jewelry making.