Polyhalite
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Polyhalite is an evaporite mineral, a hydrated sulfate of potassium, calcium and magnesium with formula: K₂Ca₂Mg(SO₄)₄·2H₂O. Polyhalite crystallizes in the triclinic system, although crystals are very rare. The normal habit is massive to fibrous. Wikipedia
2V angle: Measured: 60° to 62°
Color: Colorless, white, gray; often salmon-pink to brick-red from included iron oxide
Crystal class: Pinacoidal (1); (same H-M symbol)
Crystal habit: Typically fibrous, foliated, massive; rarely as tabular crystals; pseudo-orthorhombic
Crystal system: Triclinic
Formula (repeating unit): K2Ca2Mg(SO4)4·2H2O
Fracture: Conchoidal