Lusakite, a Cobalt-Bearing Silicate from Northern Rhodesia

A. C. Skerl, F. A. Bannister and A. W. Groves
Rhodesian Beit Railway Fellow at the Royal School of Mines, London
Assistant-Keeper in the Mineral Department of the British Museum of Natural History
Geochemistry Department, Imperial College of Science and Technology, London

Summary: Lusakite is a cobalt-bearing variety of staurolite from Northern Rhodesia and has been named after the new capital of that colony. The orthorhombic crystals have unit-cell dimensions a 7·86, b 16·62, c 5·65 Å. (a: b: c = 0·473: 1: 0·340), space-group Vh17, and the unit cell contains 8[RO.Al2SiO5], where R = Fe,Co,Ni,Mg,Al,H. The empirical formula is H2O.4(Fe,Co,Ni,Mg)O.9(Al,Fe)2O3.8SiO2. Hardness 7 ½ specific gravity 3·767, n about 1·74. The following striking features justify the new name: It is the only silicate mineral containing a significant amount of cobalt (CoO 8·48 %). An intense cobalt-blue colour best seen in thin sections under the microscope. Strong pleochroism from light cobalt-blue to deep violet-blue. It has been formed by the metasomatic replacement of kyanite.

Mineralogical Magazine; September 1934 v. 23; no. 146; p. 598-606; DOI: 10.1180/minmag.1934.023.146.03
© 1934, The Mineralogical Society
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