Sulfate crust is a zone observed in the axial (central) parts of burning

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...

dumps and related sites. It is a zone built mainly by anhydrous

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...

minerals, such as

godovikovite Godovikovite is a rare sulfate mineral with the chemical formula: (NH4)Al(SO4)2. Aluminium can partially be substituted by iron. Hydration of godovikovite gives the ammonium alum, tschermigite. The mineral forms cryptocrystalline, often porous, ...

and

millosevichite Millosevichite is a rare sulfate mineral with the chemical formula Al2(SO4)3. Aluminium is often substituted by iron. It forms finely crystalline and often porous masses. It was first described in 1913 for an occurrence in Grotta dell'Allume, Por ...

. The outer zone can easily be hydrated giving rise to minerals like

tschermigite Tschermigite is a mineral form of ammonium alum, formula N H4 Al( S O4)2·12(H2O). It is found in burning coal seams, bituminous shale and fumarole A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet fro ...

and

alunogen Alunogen (from French ''alun'', “ alum”), also called feather alum and hair salt is a colourless to white (although often coloured by impurities, such as iron substituting for aluminium) fibrous to needle-like aluminium sulfate mineral. It has ...

. The zone forms due to interaction with hot (even around 600 °C) coal-derived gases (mainly and ) with the "sterile" material (i.e. shales and other rocks serving as the source of , , and other cations) in case of the lack of vents for the gases to escape into the atmosphere.Sokol E. V., Maksimova N. V., Nigmatulina E. N., Sharygin V. V. and Kalugin V. M. 2005: Combustion metamorphism. Publishing House of the SB RAS, Novosibirsk

References

{{sulfate-mineral-stub Coal mining Combustion Sulfate minerals

See also

References