Class: Silicates
Group: Pyroxene
Original description: 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: 30—31 [
view in ‘Library’].
Type locality: Utö mines, Utö, Södermanland, Sweden.
Type material: unknown.
Etymology: from the Greek for reduced to ashes, alluding to the greyish white mass that is formed when the mineral is ignited.
Distribution: Afghanistan: Laghman; Brazil: Minas Gerais; Madagascar; Sweden; USA: from the Pala district, San Diego Co., California; at Hiddenite, Alexander Co., North Carolina; Zimbabwe (
Anthony et al., 2001—2005).
Chemistry
LiAlSi2O6
Essential elements: lithium (Li), oxygen (O), aluminium (Al), silicon (Si).
Crystal data
Crystallography: monoclinic — prismatic.
Crystal habit: crystals prismatic, typically flattened and striated, to 12.5 m and 54 t; common ly massive.
Twinning: common on {100} (
Anthony et al., 2001—2005).
Optical properties
Colour: colourless, greenish white, greyish white, yellowish green, emerald-green, yellow, pink, violet, may be bicoloured; colourless in thin section (
Anthony et al., 2001—2005).
Diaphaneity: transparent to translucent (
Anthony et al., 2001—2005).
Lustre: vitreous (
Arem, 1987: 179).
Refractive index: 1.657—1.681 — anisotropic [biaxial (+)] (
Lazzarelli, 2012).
Birefringence: 0.014—0.016.
Dispersion: 0.017 (
Arem, 1987: 179).
Pleochroism: X = purple to green; Z = colourless (
Anthony et al., 2001—2005).
Material from ‘Repository’
3 specimens: 0454 — 9.40 ct, no precise locality [Africa];
0443 — 5.07 ct, no precise locality [Africa];
0146 — 7.25 ct, Afghanistan.
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