Enstatite

Class: Silicates

In peridotites, ultramafic inclusions in alkalic olivine basalts and kimberlite; in regionally metamorphosed rocks; common in chondrite, achondrite, and iron meteorites (Anthony et al., 2001—2005).

Enstatite — specimen 0046, photo © NMNHS

Original description: ‘Enstatit’ Kenngott, A., 1855. Mineralogische Notizen, betreffend die bekannten Species: Karstenit, Dolomit, Millerit, Turmalin, Galaktit, Wasser, Plagionit, Diopsid, Zinkit, Calcit und Felsöbanyt, sowie zwei neue: den Enstatit im Geschlechte der Augit-Spathe und den Pseudophit im Geschlechte der Serpentin-Steatite — Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften 16: 162—170 [view in ‘Library’].

Type locality: unknown.

Type material: unknown.

Etymology: from the Greek for opponent, in allusion to its refractory nature under the blowpipe.

Distribution: Austria: Styria; Czech Republic; Germany; Norway; Sri Lanka; Tanzania: Mbeya; USA (Anthony et al., 2001—2005).

Chemistry

Mg2Si2O6

Essential elements: oxygen (O), magnesium (Mg), silicon (Si).

Crystal data

Crystallography: orthorhombic — dipyramidal. Crystal habit: crystals prismatic, to 40 cm; commonly lamellar, fibrous, or massive. Twinning: simple and lamellar on {100} (Anthony et al., 2001—2005).

Physical properties

Cleavage: good, {210}; partings on {100} and {010} (Anthony et al., 2001—2005). Fracture: uneven (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 5.5 (Lazzarelli, 2012). Density: 3.2—3.25 g/cm3 (Lazzarelli, 2012). Luminescence: none (Arem, 1987: 86).

Optical properties

Colour: white, greyish, yellowish, greenish, olive-green, brown; colourless in thin section (Anthony et al., 2001—2005). Diaphaneity: transparent to opaque (Anthony et al., 2001—2005). Lustre: vitreous (Arem, 1987: 86). Refractive index: 1.65—1.68 — anisotropic [biaxial (+)] (Lazzarelli, 2012). Birefringence: 0.009—0.012. Dispersion: none. Pleochroism: none.

Material from ‘Repository’

1 specimen: 0046 — 2.98 ct, Tanzania.

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