Enstatite

Enstatite is among the pyroxene family - a number of magnesium to iron rich silicates. Crystals occur as short prisms, but they are rare: most gem-quality material is faceted from rolled pebbles. Cuttable enstatite varies in olive-green, for an iron-rich brownish green. An excellent emerald green variety, coloured by chromium, also occurs.
Enstatite is usually found with kimberlites in South Africa. Brownish green enstatite can be found in Burma, Norway, and California (USA). Some Sri Lankan and Indian enstatite is chatoyant. Additionally, it occurs in the United States, Switzerland, Greenland, Scotland, Japan and the first kind USSR.

Properties

Chemical Composition: 

Silicate of Magnesium and Iron - (Mg,Fe)SiO₃. Increasing iron content changes into Hypersthene.

Classification / Type: 

Enstatite belongs to the orthopyroxene group. Of gem interest are enstatite, bronzite, hypersthene (increasing iron content) and the intermediate series. As a result there is a variation in properties, with higher values for stones with higher iron content.

Colors / Varieties: 

• Colorless, green, brownish green, yellowish green, brown, gray.
• Chatoyant and 6-Ray Star.
• Bronzite: a variety of enstatite - hypersthene, brown with fibrous inclusions.

Crystal System / Forms: 

Orthorhombic System / Prismatic crystals; twinning is common.

Hardness: 

5 - 6 (Enstatite - Hypersthene)

Specific Gravity: 

• Enstatite: 3.20 - 3.30
• Hypersthene: 3.40 - 3.50

Cleavage / Fracture: 

Distinct 2 directional prismatic cleavage; parting / Uneven fracture.

Optic Character: 

• Enstatite: Biaxial positive
• Hypersthene: Biaxial negative

Lustre: 

Vitreous

Refractive Index / Birefringence: 

• Enstatite: 1.663 - 1.673 / 0.010
• Hypersthene: 1.673 - 1.683 and 1.715 - 1.731

Pleochroism: 

Moderate: green / yellowish green / brownish green

Dispersion: 

-

Magnification: 

Parting planes and cleavage cracks, liquid fingerprints and crystal inclusions.

U.V. Fluorescence: 

Inert.

Spectrum: 

Strong lines at 505nm, 550nm, 483nm, 459nm, 449nm, 425nm.

Cause of Color: 

Iron (increasing iron content changes into hypersthene)

Treatment (Enhancement): 

-

Specific Tests & Remarks: 

-

Synthesis: 

-

Simulants (with key separation tests): 

Diopside (R.I., birefringence), Kornerupine (spectrum, pleochroism), Sillimanite (R.I., birefringence, spectrum), Moldavite (optic character).

Geological Occurrence: 

Common in basic and ultrabasic rocks and metamorphic rocks.

Sources: 

Myanmar, Sri Lanka, India, South Africa, Tanzania, U.S.A., Norway, Greenland.

Cuts & Uses: 

Facetted cuts, cabochons, beads, etc.