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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).
Diaspore — specimen 0209
Diaspore — specimen 0209, photo © NMNHS

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.



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).

Physical properties

Cleavage: on {010} perfect, on {110} distinct, on {100} in traces (Anthony et al., 2001—2005). Fracture: conchoidal (Anthony et al., 2001—2005). Tenacity: very brittle (Anthony et al., 2001—2005). Hardness: 6.5—7 (Arem, 1987: 81). Density: 3.3—3.4 g/cm3 (Lazzarelli, 2012). Luminescence: Turkish stones fluoresce green in SW (Arem, 1987: 82).

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’

3 specimens: 0209 — 0.60 ct, Turkey; 0464 — 0.76 ct, Turkey; 0219 — 0.76 ct, Turkey.

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