nag mtshur

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ནག་མཚུར
mineral used for cleaning gold [JV]

black color producing mtshur zhig [IW]

(med) Black or yellow Fibroferrite, Ferric sulfate Fe³⁺ (SO₄) (OH)·5H₂O (Drungtso 1999, Phrin Las 1987, Yeshi 2018). Synonyms : nag tshur, ser tshur, tshur nag, tshur ser, sho 'na ka (Drungtso 1999, Yeshi 2018). Yellow fibroferrite corresponds to the description of Fibroferrite : of yellow, yellowish-green to green-grey color, a fibrous aggregation containing iron (mindat.org). 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. The book, Chemistry, Inorganic & Organic, with Experiments, by Bloxam is a published, reliable reference for the composition of black vitriol, and it states on page 513, "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 iron (II) sulfates, mostly iron or copper (wikipedia) Johannes Schmidt (talk) 11:30, 25 November 2021 (UTC)