Jeremejevite

Class: Borates

A rare late hydrothermal mineral formed in granitic pegmatites (Anthony et al., 2001—2005). One of the rarest gemstones.

Jeremejevite — specimen 0586, photo © NMNHS

Original description: ‘Jéréméiéwite’ Damour, A. A., 1883. Note sur un borate d’alumine cristallisé, de la Sibérie. Nouvelle espèce minérale — Bulletin de la Société Minéralogique de France 6: 20—23 [view in ‘Library’].

Type locality: Soktuy, Nerchinsk, Zabaykalsky Krai, Russia.

Type material: Mining Institute, Saint Petersburg, Russia, 412/1 (Anthony et al., 2001—2005).

Etymology: honours Pavel Vladimirovich Eremeev, Russian mineralogist and crystallographer.

Distribution: Namibia: fine gem quality crystals from Erongo Mountains; Russia: large crystals from Zabaykalsky Krai, Nerchinsk, Soktuy; Tajikistan: Pamir (Anthony et al., 2001—2005).

Chemistry

Al6(BO3)5(F,OH)3

Essential elements: hydrogen (H), boron (B), oxygen (O), fluorine (F), aluminium (Al).

Crystal data

Crystallography: hexagonal — dipyramidal. Crystal habit: crystals are typically hexagonal prismatic {1120}, may be tapered by vincinal forms, with pyramidal {1011} termination, to 10 cm (Anthony et al., 2001—2005).

Physical properties

Cleavage: none (Arem, 1987: 118). Fracture: conchoidal (Arem, 1987: 118). Tenacity: no data. Hardness: 6.5—7 (Arem, 1987: 118). Density: 3.28—3.31 g/cm3 (Arem, 1987: 118). Luminescence: none (Arem, 1987: 118). Other: piezoelectric.

Optical properties

Colour: colourless, pale yellowish brown, pale to dark cornflower-blue; colourless to pale blue in transmitted light (Anthony et al., 2001—2005). Diaphaneity: transparent (Anthony et al., 2001—2005). Lustre: vitreous (Arem, 1987: 118). Refractive index: 1.638—1.65 — anisotropic [uniaxial (-)] (Lazzarelli, 2012). Birefringence: 0.007—0.009. Dispersion: distinct (Anthony et al., 2001—2005). Pleochroism: colourless to pale blue-violet if coloured (Anthony et al., 2001—2005).

Material from ‘Repository’

1 specimen: 0586 — 0.14 ct, Namibia, Erongo, Mount Erongo.

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