Polyhalite
Polyhalite is an evaporite mineral, a hydrated sulfate of potassium, calcium and magnesium with formula: K2Ca2Mg(SO4)4·2(H2O). Polyhalite crystallizes in the triclinic system although crystals are very rare. The normal habit is massive to fibrous. It is typically colorless, white to gray, although it may be brick red due to iron oxide inclusions. It has a Mohs hardness of 3.5 and a specific gravity of 2.8.
It occurs in sedimentary marine evaporites and is a major potassium ore mineral in the Carlsbad Deposits of New Mexico.
Polyhalite was first described in 1818 for specimens from its type locality in Salzberg, Austria. The name is from the Greek polys hals for many salts.
It has no connection to the sodium halide mineral halite other than that both are evaporite minerals.
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