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Violarite (Fe2+Ni23+S4) is a supergene sulfide mineral associated with the weathering and oxidation of primary pentlandite nickel sulfide ore minerals. Violarite crystallises in the isometric system, with a hardness of 4.5 to 5.5 and a specific gravity of about 4, is dark violet grey to copper-red, often with verdigris and patina from associated copper and arsenic sulfides, and is typically in amorphous to massive infill of lower saprolite ultramafic lithologies. Violarite has a characteristic violet colour, hence the name from the Latin 'violaris' alluding to its colour especially when viewed in polished section under a microscope. == Paragenesis == Violarite is formed by oxidisation of primary sulfide assemblages in nickel sulfide mineralisation. The process of formation involves oxidation of Ni2+ and Fe2+ which is contained within the primary pentlandite-pyrrhotite-pyrite assemblage. Violarite is produced at the expense of both pentlandite and pyrrhotite, via the following basic reaction; Pentlandite + Pyrrhotite --> Violarite + Acid :(Fe,Ni)9S8 + Fe(1-x)S + O2 → Fe2+Ni23+S4 + H2SO3 Violarite is also reported to be produced in low-temperature metamorphism of primary sulfides, though this is an unusual paragenetic indicator for the mineral. Continued oxidation of violarite leads to replacement by goethite and formation of a gossanous boxwork, with nickel tending to remain as impurities within the goethite or haematite, or rarely as carbonate minerals. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「violarite」の詳細全文を読む スポンサード リンク
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