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Category Sulfate minerals
(repeating unit)
Strunz classification 7.AC.10
Crystal system Cubic
Crystal class Tetartoidal (23)
H-M symbol: (23)
Unit cell a = 9.99 Å; Z = 2
Color White to gray
Crystal habit Equant grains and crusts
Cleavage None
Fracture Uneven
Mohs scale hardness 2
Luster Vitreous
Diaphaneity Transparent to nearly opaque
Specific gravity 2.52 (calculated)
Optical properties Isotropic
Refractive index n = 1.550
Alters to Readily hygroscopic
References [1][2][3]

Efremovite is a rare ammonium sulfate mineral with the chemical formula: (NH4)2Mg2(SO4)3. It is a white to gray cubic mineral.[3] 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.[4][5]

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.[2] It occurs in association with native sulfur, kladnoite (it), mascagnite, and boussingaultite.[3]


  1. ^ Efremovite, Webmineral.com
  2. ^ a b Efremovite, MinDat.org 
  3. ^ a b c Handbook of Mineralogy
  4. ^ Chesnokov B. V. and Shcherbakova E. P. 1991: Mineralogiya gorelykh otvalov Chelyabinskogo ugolnogo basseina - opyt mineralogii tekhnogenesa. Nauka, Moscow
  5. ^ Jambor J. L. and Grew E. S. 1991: New mineral names. American Mineralogist, 76, pp. 299-305