Class: Oxides & hydroxides
Group: Diaspore
A final product of
diagenesis in
bauxite deposits formed by the tropical weathering of alumino-silicate rocks; from hydrothermal alteration of aluminous minerals; a hydrothermal mineral in some alkalic
pegmatites (
Anthony et al., 2001—2005). The largest faceted specimen is a 157.66 carat from Turkey (
Arem, 1987: 82).
Original description: Haüy, R. J., 1801. VII. Diaspore (m.), c’est-à-dire, qui se disperse — Traité de Minéralogie 4: 358—360 [
view in ‘Library’].
Type locality: Mramorskiy Zavod, Kosoi Brod, Yekaterinburg, Sverdlovsk District, Urals, Russia.
Type material: Muséum national d’Histoire naturelle, Paris, France (
Anthony et al., 2001—2005).
Etymology: from the Greek word
διασπείρειυ (diaspeireiu), to scatter, in allusion to the usual decrepitation in the blowpipe flame.
Distribution: many localities; some prominent ones include: Greece: islands of Naxos and Samos; Russia: Urals, Sverdlovsk District, Kosoy Brod; South Africa: Northern Cape; Switzerland: Ticino, Campolungo; Turkey: Muğla; USA: California, Mono Co., White Mountains, in the Champion mine (
Anthony et al., 2001—2005). The facetable material comes mainly from Turkey.
Chemistry
AlO(OH)
Essential elements: hydrogen (H), oxygen (O), aluminium (Al).
Crystal data
Crystallography: orthorhombic — dipyramidal.
Crystal habit: crystals platy on {010} and elongated to acicular along [001], to 40 cm, foliated, scaly, massive.
Twinning: on {021}, to form heart-shaped twins or pseudohexagonal aggregates; on {061}, uncommon (
Anthony et al., 2001—2005).
Optical properties
Colour: colourless, white, pale grey, greenish grey, brown, pale yellow, pink, lilac; may show a colour change from brownish green in daylight to raspberry pink in artificial light (
Anthony et al., 2001—2005).
Diaphaneity: transparent to translucent (
Anthony et al., 2001—2005).
Lustre: adamantine, vitreous (
Anthony et al., 2001—2005).
Refractive index: 1.702—1.75 — anisotropic [biaxial (+)] (
Lazzarelli, 2012).
Birefringence: 0.048.
Dispersion: weak.
Pleochroism: in thick plates may be reddish brown to reddish violet; greyish green to green (
Anthony et al., 2001—2005).
Material from ‘Repository’
