Efremovite
A rare white ammonium-magnesium sulfate crystallizing in the crusts of burning coal dumps.
Intro adapted from Wikipedia (CC BY-SA).
Efremovite is an IMA-recognized mineral species in the sulfate class, with the chemical formula (NH₄)₂Mg₂(SO₄)₃.
It crystallizes in the cubic crystal system (space group P2_13). It is a member of the Langbeinite structural group.
Key properties: Mohs hardness 2; specific gravity 2.52; Vitreous luster.
IMA symbol Efr, IMA status: approved, named in 1987.
Occurs as crusts on burning coal mine dumps, formed by the reaction of combustion gases with carbonate rocks.
It is found associated with Sulfur, kladnoite, mascagnite, boussingaultite.
The mineral was named to honor Dr. Ivan Antonovich Yefremov (1907–1972), Russian geologist and science fiction writer.