Danburite

Class: Silicates

In granite and metamorphosed carbonate rocks associated with hydrothermal activity (Anthony et al., 2001—2005).

Danburite — specimen 0501, photo © NMNHS

Original description: Shepard, C. U., 1839. Notice of Danburite, a new Mineral Species — American Journal of Science and Arts 35: 137—139 [view in ‘Library’].

Type locality: Danbury, Fairfield Co., Connecticut, USA.

Type material: unknown.

Etymology: for the type locality at Danbury, Connecticut, USA.

Distribution: Bolivia: Cochabamba; Madagascar; Mexico: Charcas; Myanmar: Mogok district; Russia: Urals; Dalnegorsk; USA: at Danbury, Connecticut (Anthony et al., 2001—2005).

Chemistry

CaB2(SiO4)2

Essential elements: boron (B), oxygen (O), silicon (Si), calcium (Ca).

Crystal data

Crystallography: orthorhombic — dipyramidal. Crystal habit: crystals prismatic, rhomboidal to square in cross section, to 50 cm; also as disseminated masses (Anthony et al., 2001—2005).

Physical properties

Cleavage: indistinct on {001} (Anthony et al., 2001—2005). Fracture: uneven to subconchoidal (Arem, 1987: 78). Tenacity: brittle (Arem, 1987: 78). Hardness: 7 (Arem, 1987: 78). Density: 2.97—3.03 g/cm3 (Lazzarelli, 2012). Luminescence: none.

Optical properties

Colour: colourless, white, wine-yellow, yellowish brown, greenish; colourless in thin section (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous to greasy (Arem, 1987: 78). Refractive index: 1.627—1.639 — anisotropic [biaxial (+/-)] (Lazzarelli, 2012). Birefringence: 0.006. Dispersion: 0.017 (Arem, 1987: 78). Pleochroism: none (Arem, 1987: 78).

Material from ‘Repository’

7 specimens: 0327 — 0.80 ct, Tanzania, Dodoma; 0122 — 0.41 ct, Mexico, Charcas; 0234 — 0.81 ct, Mexico, Charcas; 0546 — 0.46 ct, Mexico, Charcas; 0485 — 1.01 ct, Mexico; 0501 — 1.05 ct, Mexico, Charcas; 0502 — 0.74 ct, Mexico, Charcas.

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