Various chemical staining techniques are used to identify minerals. The procedure followed is to etch the specimen, and then to expose it to a range of organic and/or inorganic compounds which form distinctive coloured complexes with certain minerals. Feldspars can be identified by etching with hydrofluoric acid and then treating with sodium cobaltinitrate, barium chloride, and potassium acid rhodizonate. Plagioclases stain red and K-feldspars are stained yellow after this treatment. For carbonates, a range of stains, including alizarin red S, Feigl's solution, potassium ferricyanide alizarine cyanic green, and titan yellow are used. A number of staining combinations allow the differentiation of calcite, high-Mg calcite, dolomite, anhydrite, and gypsum.
Subjects: Earth Sciences and Geography.