Polyhalite is an evaporite mineral, a hydrated sulfate of potassium, calcium and magnesium with formula: . 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

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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

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deposits of New Mexico. It is also present as a 2–3% contaminant of Himalayan salt. Polyhalite was first described in 1818 for specimens from its type locality in Salzburg, Austria. The name comes from the German ''Polyhalit'', which comes from the Ancient Greek words (''polys'') and ' (''hals''), which mean "many" and "salt", and the German ending ''-it'' (which comes from the Latin ending -ites, which originally also came from Greek), which is used like the English ending ''-ite'' to form the names of certain chemical compounds. Despite the similarity in names between ''polyhalite'' and '' halite'' (the naturally occurring form of table salt), their only connection is that both are evaporite minerals. The use of the Greek words for ''many'' and ''salt'' in polyhalite is due to polyhalite consisting of several metals that can form salts in the more general sense of the word salt used in chemistry.

Production

The only polyhalite mined in the world comes from a layer of rock over below the North Sea off the North Yorkshire coast in the UK. Deposited 260 million years ago, it lies below the potash seam at the Boulby Mine. In 2010, the first mining operations of the polyhalite mineral commenced at Boulby Mine, the mine is currently the only producer of polyhalite which is marketed by Israel Chemicals as Polysulphate. In 2016, Sirius Minerals announced plans for the Woodsmith Mine, a new polyhalite mine in the area. In March 2020, the project was taken over by Anglo American plc.

Composition and use

Polyhalite is used as a fertilizer since it contains four important nutrients and is low in chloride: *48% as sulfate *14% as from sulfate of potash *6% MgO as from magnesium sulfate *17% CaO as from calcium sulfate Polyhalite crystal structure

References

{{reflist Magnesium minerals Calcium minerals Potassium minerals Sulfate minerals Triclinic minerals Evaporite Potash Minerals in space group 2