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Class: Silicates

In gneisses, schists, included pegmatites, and quartz veins, from regional metamorphism of sedimentary rocks (Anthony et al., 2001—2005).
Kyanite — specimen 0481
Kyanite — specimen 0481, photo © NMNHS

Original description: ‘Cyanit’ Hoffmann, C. A. S., 1789. Mineralsystem des Herrn Inspektor Werners mit dessen Erlaubnis herausgegeben von C. A. S. Hoffmann — Bergmannisches Journal 1: 377, 397 [view in ‘Library’].

Type locality: unknown.

Type material: Technische Universität Bergakademie, Freiberg, Germany, 22491 (Anthony et al., 2001—2005).

Etymology: from the Greek for blue, in allusion to its common dark blue colour.

Distribution: widely distributed, even in good crystals: Austria: Tirol, Zillertal; Brazil: a number of localities in Minas Gerais; Russia: Yekaterinburg, Urals; Switzerland: Ticino (Anthony et al., 2001—2005).



Essential elements: oxygen (O), aluminium (Al), silicon (Si).

Crystal data

Crystallography: triclinic — pinacoidal. Crystal habit: crystals bladed and tabular on {100}, to 0.5 m; typically bent or twisted. Twinning: lamellar on {100} (Anthony et al., 2001—2005).

Physical properties

Cleavage: perfect on {100}, good on {010}, parting on {001} (Anthony et al., 2001—2005). Fracture: splintery (Anthony et al., 2001—2005). Tenacity: no data. Hardness: 4—7 (Lazzarelli, 2012). Density: 3.55—3.7 g/cm3 (Lazzarelli, 2012). Luminescence: none.

Optical properties

Colour: blue, white, rarely green, grey, yellow, pink, black, can be zoned; colourless to pale blue in thin section (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous to pearly (Arem, 1987: 121). Refractive index: 1.71—1.735 — anisotropic [biaxial (-)] (Lazzarelli, 2012). Birefringence: 0.012—0.033. Dispersion: 0.02 (Arem, 1987: 121). Pleochroism: weak; in thick sections, X = colourless; Y = violet-blue; Z = cobalt blue (Anthony et al., 2001—2005).

Material from ‘Repository’

1 specimen: 0481 — 0.59 ct, Cambodia.

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