nag mtshur
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ནག་མཚུར
mineral used for cleaning gold [JV]
black color producing mtshur zhig [IW]
(med) Fibroferrite, Ferric sulfate Fe3+ (SO4) (OH)·5H2O (Yeshi 2018), Black fibroferrite, Black vitriol (Drungtso 1999, Phrin Las 1987). Synonyms : nag tshur, tshur nag (Drungtso 1999, Yeshi 2018).
Black fibroferrite or black vitriol (Drungtso 1999) may be a mixture : "Many websites state "black vitriol is a mixture of iron sulfate and iron sulfite", but none gives a reference of any sort. 'Chemistry, Inorganic & Organic, with Experiments', by Bloxam is a reference for the composition of black vitriol, "The formula of black vitriol may be written [CuMgFeMnCoNi]SO4·7H2O, the six isomorphous metals being interchangeable without altering the general character of the salt." (wikipedia). Vitriol itself is an ancient and now obsolete name for several hydrated metal sulfates, mostly iron or copper (wikipedia) Johannes Schmidt (talk) 11:30, 25 November 2021 (UTC)