Efremovite is a rare ammonium sulfate mineral with the chemical formula: (NH4)2Mg2(SO4)3. It is a white to gray cubic mineral.[4] This anhydrous sulfate occurs as constituent in sulfate crusts of burning coal dumps. It is hygroscopic and when exposed to humid air it slowly converts to the hydrate form, boussingaultite.[5][6]

Efremovite
General
CategorySulfate minerals
Formula
(repeating unit)
(NH4)2Mg2(SO4)3
IMA symbolEfr[1]
Strunz classification7.AC.10
Crystal systemCubic
Crystal classTetartoidal (23)
H-M symbol: (23)
Unit cella = 9.99 Å; Z = 2
Identification
ColorWhite to gray
Crystal habitEquant grains and crusts
CleavageNone
FractureUneven
Mohs scale hardness2
LusterVitreous
DiaphaneityTransparent to nearly opaque
Specific gravity2.52 (calculated)
Optical propertiesIsotropic
Refractive indexn = 1.550
Alters toReadily hygroscopic
References[2][3][4]

It was first described in 1989 for an occurrence in the Chelyabinsk coal basin, Southern Urals, Russia. It was named for Russian geologist Ivan Antonovich Yefremov (1907–1972). It has also been reported from several coal mining areas across Europe.[3] It occurs in association with native sulfur, kladnoite [it], mascagnite, and boussingaultite.[4]

References

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Efremovite, Webmineral.com
  3. ^ a b Efremovite, Mindat.org
  4. ^ a b c Handbook of Mineralogy
  5. ^ Chesnokov B. V. and Shcherbakova E. P. 1991: Mineralogiya gorelykh otvalov Chelyabinskogo ugolnogo basseina - opyt mineralogii tekhnogenesa. Nauka, Moscow
  6. ^ Jambor J. L. and Grew E. S. 1991: New mineral names. American Mineralogist, 76, pp. 299-305