English: Polyhalite rock from the Permian of New Mexico, USA. (4.3 cm across at its widest)

A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 5100 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.

The sulfate minerals all contain one or more sulfate anions (SO4-2).

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 hydrous potassium calcium magnesium sulfate (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.

The New Mexico polyhalite rock sample shown here is from the subsurface, Permian-aged Salado Formation, which is a succession of interbedded rock salt (halitite), rock anhydrite, polyhalite rock, and fine-grained siliciclastic beds.

Stratigraphy: Salado Formation, Ochoan Stage, upper Upper Permian

Locality: Carlsbad Potash District, east of Carlsbad, Delaware Basin, southeastern New Mexico, USA

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Photo gallery of polyhalite:

http://www.mindat.org/gallery.php?min=3259