| Langbeinite | |
| Category: | Sulfate mineral |
| Formula: | K2Mg2(SO4)3 |
| Imasymbol: | Lbn[1] |
| Strunz: | 7.AC.10 |
| System: | Cubic |
| Class: | Tetartoidal (23) (same H-M symbol) |
| Symmetry: | P213 |
| Unit Cell: | a = 9.92 Å; Z = 4 |
| Color: | Colorless with pale shades of yellow, pink, red, green, gray |
| Habit: | As nodules, disseminated grains, bedded massive |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Mohs: | 3.5–4 |
| Luster: | Vitreous |
| Diaphaneity: | Transparent |
| Gravity: | 2.83 |
| Opticalprop: | Isotropic |
| Refractive: | n = 1.5329–1.5347 |
| Solubility: | 280 g/L (20°C);[2] Slowly dissolves in water[3] |
| Other: | 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).