Langbeinite

Langbeinite
General
Category	Sulfate mineral
Formula	K2Mg2(SO4)3
IMA symbol	Lbn[1]
Strunz classification	7.AC.10
Crystal system	Cubic
Crystal class	Tetartoidal (23) (same H-M symbol)
Space group	P213
Unit cell	a = 9.92 Å; Z = 4
Identification
Color	Colorless with pale shades of yellow, pink, red, green, gray
Crystal habit	As nodules, disseminated grains, bedded massive
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	280 g/L (20°C);[2] Slowly dissolves in water[3]
Other characteristics	Piezoelectric
References	[4][5][6]

Langbeinite is a potassium magnesium sulfate mineral with the chemical formula K₂Mg₂(SO₄)₃. Langbeinite crystallizes in the isometric-tetartoidal (cubic) 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.^[4]

The mineral is an ore of potassium and occurs in marine evaporite deposits in association with carnallite, halite, and sylvite.^[4]

It was first described in 1891 for an occurrence in Wilhelmshall, Halberstadt, Saxony-Anhalt, Germany, and named for A. Langbein of Leopoldshall, Germany.^[4][5]

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

Related substances include hydrated salts leonite (K₂Mg(SO₄)₂·4H₂O) and picromerite (K₂Mg(SO₄)₂·6H₂O).