Scheelite

Class: Sulphates
Group: Scheelite

A component of contact metamorphic tactite; in high-temperature hydrothermal veins and greisen; less common in granite pegmatites and medium-temperature hydrothermal veins; alluvial (Anthony et al., 2001—2005). Very rare gemstone.

Scheelite — specimen 0431, photo © NMNHS

Original description: ‘Scheelit’ von Leonhard, K. C., 1821. Scheelit — Handbuch der Oryktognosie, Heidelberg: 594—596 [view in ‘Library’].

Type locality: Bispbergs, Säter, Dalarna, Sweden.

Type material: unknown.

Etymology: named after Swedish chemist Carl Wilhelm Scheele, who discovered tungsten.

Distribution: an important ore of tungsten, with many localities: Brazil: Minas Gerais; Canada; China; Germany: Altenberg and Schwarzenberg, Saxony; Italy: Piedmont; Mexico; Namibia; Russia; South Korea; Sweden: Dalarna; Vietnam (Anthony et al., 2001—2005).

Chemistry

Ca(WO4)

Essential elements: oxygen (O), calcium (Ca), tungsten (W).

Crystal data

Crystallography: tetragonal — dipyramidal. Crystal habit: crystals are typically pseudo-octahedral {011} or {112}, with modifying forms {001}, {013}, {121}, to 32 cm; commonly granular, massive. Twinning: {110}, common, penetration and contact twins, composition plane {110} or {001} (Anthony et al., 2001—2005).

Physical properties

Cleavage: {101}, distinct; on {112}, interrupted; on {001}, indistinct (Anthony et al., 2001—2005). Fracture: uneven to conchoidal (Arem, 1987: 168). Tenacity: brittle (Arem, 1987: 168). Hardness: 4.5—5 (Lazzarelli, 2012). Density: 5.9—6.3 g/cm3 (Arem, 1987: 167). Luminescence: bright bluish white cathodoluminescence and fluorescence under SW UV and X-rays (Anthony et al., 2001—2005).

Optical properties

Colour: colourless, white, grey, brown, pale yellow, yellow-orange, pale shades of orange, red, green; may be compositionally colour zoned (Anthony et al., 2001—2005). Diaphaneity: transparent to opaque (Anthony et al., 2001—2005). Lustre: vitreous to adamantine (Anthony et al., 2001—2005). Refractive index: 1.918—1.936 — anisotropic [uniaxial (+)] (Lazzarelli, 2012). Birefringence: 0.01—0.018. Dispersion: 0.038. Pleochroism: none.

Material from ‘Repository’

1 specimen: 0431 — 0.39 ct, China.

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