Polyhalite

polyhalite

carnallite

langbeinite

vanthoffite

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Formula: K₂Ca₂Mg(SO₄)₄.2H₂O
Hydrated sulphate
Crystal System: Triclinic
Specific gravity: 2.78 measured, 2.763 calculated
Hardness: 2½ to 3½
Streak: White
Colour: Colourless, white, pink, red, grey, colourless in transmitted light
Solubility: Decomposed by water with separation of gypsum (Dana)
Environments

Evaporite deposits
fumaroles rarely

Polyhalite is common in marine salt deposits, where it may constitute the major component; it is diagenetic in playa muds, formed from gypsum in the presence of magnesium and potassium rich solutions, and rare as a fumarolic sublimate. Associated minerals include halite, anhydrite, glauberite, carnallite, kieserite, langbeinite and vanthoffite (HOM).

Localities

The type Locality is Ischler Salzberg, Perneck, Bad Ischl, Gmunden District, Upper Austria.

At the Stassfurt Potash deposit, Saxony-Anhalt, Germany, polyhalite is abundantly disseminated in halite (Dana).

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