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Hennomartinite and kornite, two new Mn3+ rich silicates from the Wessels Mine, Kalahari, South Africa

Hennomartinite, SrMn2(Si2O7)(OH)2xH2O, is an orthorhombic disilicate of the lawsonite structure type which occurs as anhedral poikiloblasts up to 1 mm, strongly intergrown with sugilite and serandite-pectolite. The mineral is translucent in thin section, pleochroic from yellowish brown to dark red-brown and has indices of refraction greater than 1.82. The calculated density is 3.68 g/cm3. The chemical composition was determined by electron microprobe analyses and IR-spectroscopy. The trivalent character of Mn is derived from stoichiometry and bond lengths obtained from a crystal structure analyses. Kornite, (K, Na)(Na, Li)2(Mg, Mn3+, Fe3+, Li)5Si8O22(OH)2, is a monoclinic amphibole. The calculated density is 3.15 g/cm3. The mineral forms bundles of extremely fine fibers (5-20 μ in diameter), often bent, maximum fibre length 0.2 mm. The mineral is dark red to brownish-lilac, biaxial (2Vx = 88-92°)… .

hennomartinite; kornite; sugilite; lawsonite; amphibole; new mineral; Mn-silicates; Kalahari Manganese Field; South Africa

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