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Class: Silicates
Group: Pyroxene

Varieties | Names:

Typical of metamorphosed siliceous Ca, Mg-rich rocks; common in skarns, Ca, Mg-rich gneisses and schists, and some kimberlites and peridotites (Anthony et al., 2001—2005).

Original description: ‘Coccolit’ d’Andrada, J. B., 1800. Kurze Angabe der Eigenschaften und Kennzeichen einiger neuen Fossilien aus Schweden und Norwegen, nebst einigen chemischen Bemerkungen über dieselben — Allgemeines Journal der Chemie 4: 28 [view in ‘Library’].

Type locality: unknown.

Type material: unknown.

Etymology: from the Greek for double and appearance, apparently for two possible orientations of the prism zone.

Distribution: Afghanistan: Kandahar; Austria: at Schwarzenstein, Zillertal, and near Prägraten, Tirol; Canada; China: Kunlun Mountains; India: near Jaipur, Rajasthan; Italy: Piedmont; Madagascar; Pakistan; Russia: Akhmatovsk deposit, near Zlatoust, Urals; Sakha Republic, Aldan; USA: at DeKalb, New York (Anthony et al., 2001—2005).



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

Crystal data

Crystallography: monoclinic — prismatic. Crystal habit: as prismatic crystals with nearly square cross sections, to 50 cm; granular, columnar, lamellar, massive. Twinning: simple or multiple twins on {100} or {010}, common (Anthony et al., 2001—2005).

Physical properties

Cleavage: distinct on {110}; partings on {100} and probably {010} (Anthony et al., 2001—2005). Fracture: uneven to conchoidal (Arem, 1987: 82). Tenacity: brittle (Arem, 1987: 82). Hardness: 5—6 (Lazzarelli, 2012). Density: 3.22—3.4 g/cm3 (Lazzarelli, 2012). Luminescence: none.

Optical properties

Colour: colourless, white, yellow, pale to dark green, black; colourless in thin section (Anthony et al., 2001—2005). Diaphaneity: transparent to opaque (Anthony et al., 2001—2005). Lustre: vitreous or dull (Anthony et al., 2001—2005). Refractive index: 1.664—1.730 — anisotropic [biaxial (+)] (Lazzarelli, 2012). Birefringence: 0.024—0.03. Dispersion: 0.017—0.02. Pleochroism: none.

Material from ‘Repository’

2 specimens: 0541 — 0.57 ct, Tanzania; 0053 — 0.75 ct, Russia, Far Eastern District, Sakha Republic.

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