Despite the name “polyhalite”, this mineral is not a halide, and has no sodium or chlorine in it. It is one of several minerals that occur in evaporitic successions. Polyhalite is a hydrous potassium calcium magnesium sulfate mineral (K2Ca2Mg(SO4)4·2H2O). It has a nonmetallic luster, a white streak, is moderately soft, and often has a pinkish to reddish to salmon color. The pink-red-salmon colors result from the presence of finely-disseminated hematite. It typically occurs in microcrystalline masses and is associated with other evaporite minerals such as halite and anhydrite.
Polyhalite (4.3 cm across at its widest) from the subsurface Salado Formation (Ochoan Stage, upper Upper Permian) in the Carlsbad Potash District, east of Carlsbad, Delaware Basin, southeastern New Mexico, USA. The Salado Formation is a succession of interbedded halite, anhydrite, polyhalite, and fine-grained siliciclastic beds.