Hambergite

Class: Borates

An uncommon accessory mineral in granite pegmatites (Anthony et al., 2001—2005). Faceted specimens are very rare. The largest faceted stone is a 40.2 carat (Arem, 1987: 109).

Hambergite — specimen 0499, photo © NMNHS

Original description: ‘Hambergit’ Brögger, W. C., 1890. Die Mineralien der Syenitpegmatitgänge der südnorwegischen Augit- und Nephelinsyenite, 16. Hambergit — Zeitschrift für Kristallographie 16: 65—67 [view in ‘Library’].

Type locality: Salbutangen, Helgeroa, Larvik, Vestfold, Norway.

Type material: Muséum national d’Histoire naturelle, Paris, France, 10734; National Museum of Natural History, Smithsonian Institution, Washington, DC, USA, 116994; Naturhistoriska riksmuseet, Stockholm, Sweden, 332865 (Anthony et al., 2001—2005).

Etymology: honours Professor Axel Hamberg, Swedish mineralogist and geographer.

Distribution: Madagascar: Betafo, Anjanabanoana pegmatites and Myanmar can be mentioned as a primary sources for facet-grade rough.

Chemistry

Be2(BO3)(OH)

Essential elements: hydrogen (H), beryllium (Be), boron (B), oxygen (O).

Crystal data

Crystallography: orthorhombic — dipyramidal. Crystal habit: typically well-crystallised, prismatic along [001] or dipyramidal; to 30 cm. Twinning: on {110}, commonly reticulated; contact twins may be markedly hemimorphic (Anthony et al., 2001—2005).

Physical properties

Cleavage: on {010}, perfect; on {100}, good (Anthony et al., 2001—2005). Fracture: conchoidal to uneven (Arem, 1987: 109). Tenacity: brittle (Arem, 1987: 109). Hardness: 7.5 (Arem, 1987: 109). Density: 2.33—2.37 g/cm3 (Lazzarelli, 2012). Luminescence: none.

Optical properties

Colour: colourless, pale grey, pale yellow; colourless in transmitted light (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous (Anthony et al., 2001—2005). Refractive index: 1.543—1.631 — anisotropic [biaxial (+)] (Lazzarelli, 2012). Birefringence: 0.071—0.074. Dispersion: 0.015 (low). Pleochroism: none.

Material from ‘Repository’

3 specimens: 0489 — 0.26 ct, Myanmar; 0499 — 0.34 ct, Myanmar; 0487 — 0.28 ct, Myanmar.

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