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).
Chemistry
Al2SiO5
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).
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’