Enstatite

enstatite
Tumbled enstatite

Enstatite is one of the pyroxene family – a series of magnesium to iron rich silicates. Enstatite occur as short prisms, but most gem-quality material is faceted from rolled pebbles. Cuttable enstatite varies in color from grey to yellowish green or olive-green, to an iron-rich brownish green. An excellent emerald green variety, coloued 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. It also occurs in United States, Switzerland, Greenland, Scotland, Japan and the former USSR.

Cause of Color :

Iron (increasing iron content changes into hypersthene)

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.

Crystal System / Forms :

Orthorhombic System / Prismatic crystals; twinning is common.

Cuts & Uses :

Facetted cuts, cabochons, beads, etc.

Hardness : 5 - 6 (Enstatite - Hypersthene)
Lustre : Vitreous
Magnification :

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

Optic Character :
  • Enstatite: Biaxial positive
  • Hypersthene: Biaxial negative
Pleochroism : Moderate: green / yellowish green / brownish green
Refractive Index / Birefringence :
  • Enstatite: 1.663 – 1.673 / 0.010
  • Hypersthene: 1.673 – 1.683 and 1.715 – 1.731
Simulants (with separation tests) :

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

Sources :

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

Spectrum :

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

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