Efremovite is a rare ammonium

sulfate mineral The sulfate minerals are a class of minerals that include the sulfate ion () within their structure. The sulfate minerals occur commonly in primary evaporite depositional environments, as gangue minerals in hydrothermal veins and as secondary mine ...

with the chemical formula: (NH₄)₂Mg₂(SO₄)₃. It is a white to gray cubic mineral.Handbook of Mineralogy
/ref> This anhydrous sulfate occurs as constituent in sulfate crusts 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. It is

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substan ...

and when exposed to humid air it slowly converts to the hydrate form, boussingaultite.Jambor J. L. and Grew E. S. 1991: New mineral names. American Mineralogist, 76, pp. 299-305 It was first described in 1989 for an occurrence in the Chelyabinsk coal basin, Southern

Urals The Ural Mountains ( ; rus, Ура́льские го́ры, r=Uralskiye gory, p=ʊˈralʲskʲɪjə ˈɡorɨ; ba, Урал тауҙары) or simply the Urals, are a mountain range that runs approximately from north to south through western ...

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...

. It was named for Russian geologist Ivan Antonovich Yefremov (1907–1972). It has also been reported from several coal mining areas across Europe. It occurs in association with

native sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

, , mascagnite, and boussingaultite.

References

Sulfate minerals Magnesium minerals Ammonium minerals Cubic minerals Minerals in space group 198 Minerals described in 1989 {{sulfate-mineral-stub