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Category Sulfate mineral
(repeating unit)
Strunz classification 07.AC.10
Crystal symmetry Isometric tetartoidal
H-M symbol: (2 3)
Space group: P 213
Unit cell a = 9.92 Å; Z=4
Color Colorless with pale shades of yellow, pink, red, green, gray
Crystal habit As nodules, disseminated grains, bedded massive
Crystal system Cubic
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 3.5 - 4
Luster Vitreous
Diaphaneity Transparent
Specific gravity 2.83
Optical properties Isotropic
Refractive index n = 1.5329–1.5347
Solubility Slowly dissolves in water
Other characteristics Piezoelectric
References [1][2][3]

Langbeinite is a potassium magnesium sulfate mineral with formula: K2Mg2(SO4)3. Langbeinite crystallizes in the isometric - tetartoidal system as transparent colorless or white with pale tints of yellow to green and violet crystalline masses. It has a vitreous luster. The Mohs hardness is 3.5 to 4 and the specific gravity is 2.83. The crystals are piezoelectric.[1]

The mineral is an ore of potassium and occurs in marine evaporite deposits in association with carnallite, halite and sylvite.[1]

It was first described in 1891 for an occurrence in Wilhelmshall, Halberstadt, Saxony-Anhalt, Germany, and named for A. Langbein of Leopoldshall, Germany.[1][2]

Langbeinite gives its name to the Langbeinites a family of substances with the same cubic structure, a tetragonal anion, and large and small cations.

Related substances include hydrated salts Leonite (K2Mg(SO4)2) and picomerite.