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Class: Oxides & hydroxides
Group: Hematite

Varieties | Names:

Characteristic of Al-rich, Si-poor geological environments; in syenite and monzonite, and some quartz-free pegmatites; primary or a reaction product in eclogitic xenoliths in kimberlites. In regional or contact metamorphic aluminous rocks, and some advanced argillic and potassic hydrothermal alteration assemblages (Anthony et al., 2001—2005). Famous specimens: Black Star of Queensland, 733 carats from Australia, now owned by an unknown private party; Logan sapphire, 422.99 carats from Sri Lanka, in National Museum of Natural History, Smithsonian Institution, Washington.
Ruby — specimen 0276
Ruby — specimen 0276, photo © NMNHS

Original description: unknown [prehistoric].

Type locality: unknown [prehistoric].

Type material: unknown.

Etymology: derived from the Sanskrit, kuruvinda (ruby).

Distribution: many localities. Afghanistan: Jegdalek marble, near Sorobi, Laghman Province; Australia: Queensland, Anakie; Cambodia: around Bottambang and Pailin; Canada: Ontario, Bancroft and Haliburton; Greece: Naxos and Samos Islands; India: Kashmir, Zanskar district; around Mysore; Madagascar: Ampanihy, around Andranondambo and Antsiermene; Myanmar: Mogok district; South Africa: Transvaal, around the Soutpansberg; Sri Lanka: Ratnapura district; Tanzania: near Longido, and the Morogoro district; Umba Valley; Thailand: Chanthaburi and Trat; USA: Georgia, Rabun Co., Laurel Creek mine; Massachusetts, Hampden Co., Chester; Montana, Fergus Co., 25 km southwest of Utica, Yogo Gulch; New Jersey, Sussex Co., Franklin; New York, Westchester Co., Cortland district; North Carolina, Clay Co., Buck Creek, Jackson Co., Hogback Mountain (Anthony et al., 2001—2005).



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

Crystal data

Crystallography: trigonal — hexagonal scalenohedral. Crystal habit: crystals hexagonal, prismatic or steeply dipyramidal, tabular, rhombohedral, rarely acicular, typically rough, to 1 m; sectorially striated on {0001} || {1011}. Also granular, massive. Twinning: common lamellar || {1011}, may be an exsolution phenomenon. Contact or penetration twins on {0001} or {1011}, rare (Anthony et al., 2001—2005).

Physical properties

Cleavage: partings on {0001} and {1011}, from exsolved böhmite (Anthony et al., 2001—2005). Fracture: uneven to conchoidal (Anthony et al., 2001—2005). Tenacity: brittle, tough when compact (Anthony et al., 2001—2005). Hardness: 9 (Arem, 1987: 71). Density: 3.9—4.05 g/cm3 (Lazzarelli, 2012). Luminescence: none.

Optical properties

Colour: colourless, grey, brown; pink to pigeon-blood-red, orange, yellow, green, blue to cornflower blue, violet; may be colour zoned, asteriated; colourless, pale bluish or reddish in transmitted light (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: adamantine to vitreous (Anthony et al., 2001—2005). Refractive index: 1.758—1.78 — anisotropic [uniaxial (-)] (Lazzarelli, 2012). Birefringence: 0.008—0.009. Dispersion: 0.018 (low) (Arem, 1987: 71). Pleochroism: weak to none.

Material from ‘Repository’

14 specimens: 0147 — 0.02 ct, Mozambique; 0318 — 0.11 ct, Myanmar; 0276 — 0.61 ct, Tanzania, Ruvuma, Songea; 0629 — 0.12 ct, Tanzania, Ruvuma, Songea; 0654 — 0.13 ct, no precise locality [East Africa]; 0263 — 0.18 ct, Sri Lanka; 0326 — 0.20 ct, Sri Lanka; 0640 — 0.20 ct, Madagascar; 0668 — 0.31 ct, Thailand; 0646 — 0.27 ct, Madagascar; 0505 — 0.11 ct, Sri Lanka; 0223 — 0.36 ct, Madagascar, Ihorombe, Ilakaka; 0364 — 0.12 ct, no locality data; 0148 — 0.18 ct, no locality data.

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