Gemmology
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Clinozoisite

Class: Silicates
Group: Epidote

Typically in regionally metamorphosed igneous and sedimentary rocks, as well as in contact metamorphosed calcium-rich sediments; an alteration product of plagioclase feldspars (Anthony et al., 2001—2005). Faceted specimens are extremely rare.

Original description: ‘Кlinozoisit’ Weinschenk, E., 1896. Ueber Epidot und Zoisit — Zeitschrift für Kristallographie 26: 166—169 [view in ‘Library’].

Type locality: Gösleswand, Prägraten, Tyrol, Austria.

Type material: unknown.

Etymology: named for its monoclinic crystallography and the relationship to zoisite.

Distribution: Austria: Gösleswand, near Prägraten, Tyrol; Canada: from Timmins, Ontario; Czech Republic; Madagascar; Mexico; Norway: Arendal (Anthony et al., 2001—2005).

Chemistry

Ca2Al3(SiO4)3(OH)

Essential elements: hydrogen (H), oxygen (O), aluminium (Al), silicon (Si), calcium (Ca).

Crystal data

Crystallography: monoclinic — prismatic. Crystal habit: crystals prismatic, typically elongated and striated; commonly coarse to fine granular; also fibrous. Twinning: lamellar on {100}, uncommon (Anthony et al., 2001—2005).

Physical properties

Cleavage: perfect on {001} (Anthony et al., 2001—2005). Fracture: uneven (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 6—7 (Lazzarelli, 2012). Density: 3.21—3.38 g/cm3 (Lazzarelli, 2012). Luminescence: none.

Optical properties

Colour: colourless, pale yellow, pink, red, grey, green; colourless in thin section (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous. Refractive index: 1.67—1.734 — anisotropic [biaxial (+)] (Lazzarelli, 2012). Birefringence: 0.005—0.015. Dispersion: no data. Pleochroism: none.

Material from ‘Repository’

1 specimen: 0047 — 0.57 ct, Pakistan, Gilgit-Baltistan (Northern Areas), Baltistan, Skardu District.


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