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Kainite - Grube Brefeld, Tarthun, Staßfurt, Sachsen-Anhalt.jpg
Category Sulfate minerals
(repeating unit)
Strunz classification 07.DF.10
Crystal symmetry Monoclinic prismatic
H-M symbol: (2/m)
Space group: C 2/m
Unit cell a = 19.72 Å, b = 16.23 Å, c = 9.53 Å; β = 94.92°
Color Colorless; yellow, brownish, greyish-green, red, violet, blue
Crystal habit Crystal aggregates, fibrous, massive
Crystal system Monoclinic
Cleavage {001}, perfect
Fracture Splintery
Tenacity Brittle
Mohs scale hardness 2.5-3
Luster Vitreous
Streak White
Diaphaneity Transparent
Specific gravity 2.15
Optical properties Biaxial (-)
Refractive index nα = 1.494 nβ = 1.505 nγ = 1.516
Birefringence δ = 0.022
Pleochroism Visible: X = violet, Y = blue, Z = yellowish
2V angle Measured: 90°
Dispersion Weak
References [1][2][3]

Kainite (KMg(SO4)Cl·3H2O) is a mineral salt that consists of potassium chloride and magnesium sulfate and is used as a fertilizer. This mineral is dull and soft, is colored white through yellow to red and is found in the Stassfurt salt mines in Saxony, Germany. It is a natural salt occurring in irregular granular masses, and is used as a source of potassium and magnesium compounds.

Crystal structure of kainite