Hydrated arsenate containing hydroxyl
Specific gravity: 3.197 (calculated)
Colour: Sky blue to very pale blue, white, colourless
Ianbrucite is a rare arsenate that forms during the oxidation of base-metal sulphide minerals (R&M 91.1.80). To date (March 2019)
it has been found only at Tsumeb Namibia, Cumbria England and Saxony Germany (Mindat).
At the type locality, the Tsumeb Mine, Oshikoto Region, Namibia, ianbrucite occurs as a secondary mineral in the oxidised zone of a polymetallic sulphide deposit, associated with leiteite, köttigite, legrandite and adamite (HOM, Mindat).
At the Driggith mine, Caldbeck Fells, Cumbria, England, ianbrucite occurs as a late-stage supergene mineral in low-temperature lead-zinc-copper veins. It has been found scattered on quartz-dolomite matrix associated with sphalerite, chalcopyrite, köttigite and adamite. Arsenopyrite is abundant there, and its oxidation in veins that also contain primary lead, zinc and copper sulphides has produced a range of supergene arsenates. (M&M 34.8-10, Wiki).
At Potts Gill mine, Caldbeck Fells, Cumbria, England, ianbrucite has been found as crusts on fractures in blocks containing marcasite, galena, sphalerite and arsenopyrite on dolomite matrix from low-temperature lead-zinc-copper veins (M&M 34.10-11, Wiki).
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