Polyhalite is an evaporite mineral, a hydrated sulfate of

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

, calcium and

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

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

iron oxide An iron oxide is a chemical compound composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Ferric oxyhydroxides are a related class of compounds, perhaps the best known of which is rust. Iron ...

inclusions. It has a

Mohs hardness The Mohs scale ( ) of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fair ...

of 3.5 and a specific gravity of 2.8. It is used as a fertilizer. Polyhalite was first described in 1818 for specimens from its type locality in

Salzburg Salzburg is the List of cities and towns in Austria, fourth-largest city in Austria. In 2020 its population was 156,852. The city lies on the Salzach, Salzach River, near the border with Germany and at the foot of the Austrian Alps, Alps moun ...

, Austria. It occurs in sedimentary marine evaporites and is a major potassium ore mineral in the Carlsbad deposits of

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

. It is also present as a 2–3% contaminant of Himalayan salt. The only deposit currently being mined lies under

North Yorkshire North Yorkshire is a Ceremonial counties of England, ceremonial county in Northern England.The Unitary authorities of England, unitary authority areas of City of York, York and North Yorkshire (district), North Yorkshire are in Yorkshire and t ...

, UK, extending under the adjacent North Sea.

Name

The name comes from the German ''Polyhalit'', which comes from the

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), 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.

Extraction

The only polyhalite mined in the world comes from a layer of rock over below North Yorkshire and extending off the

North Sea The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium, and France. A sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Se ...

coast in the UK, deposited 260 million years ago. In 2010, the first mining operations of this polyhalite mineral layer commenced at

Boulby Mine The Boulby Mine is an underground mining operation with surface facilities located just south-east of the village of Boulby, on the north-east coast of the North York Moors, east of Loftus, North Yorkshire. It is operated by Cleveland Potash L ...

, and the mine is in 2023 the only producer of polyhalite, marketed by ICL Group Ltd. as

Polysulphate ICL Group Ltd. (Hebrew language, Hebrew: איי.סי. אל. גרופ בע"מ) (formerly Israel Chemicals Ltd., ICL) is a multi-national manufacturing concern that develops, produces and markets fertilizers, metals and other special-purpose che ...

. In 2016, Sirius Minerals announced plans for the Woodsmith Mine in the area. In March 2020, the Woodsmith project was taken over by

Anglo American plc Anglo American plc is a British Multinational corporation, multinational mining company with headquarters in London, England. It is the world's largest producer of platinum, with around 40% of world output, as well as being a major producer of ...

and construction of two 1,500 m (4,900 ft) shafts to reach the 230 feet (70 m) mineral seam was underway in 2015. These will reach a mineable area of around 25,200 hectares (62,000 acres) and Woodsmith Mine will be the deepest in Europe."North York Moors potash mine gets £1.7bn go-ahead". The Guardian. 30 June 2015. Retrieved 3 February 2016. Polyhalite extraction is expected to begin in 2027.

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 has a variety of other uses, including: Soil amendment: Polyhalite can help to improve the drainage and fertility of soil. It can also help to reduce the acidity of soil. Water treatment additive: Polyhalite can help to remove impurities from water, such as sulfates and chlorides. It can also help to soften water and make it less corrosive. Animal feed additive: Polyhalite can be added to animal feed to improve the nutritional value of the feed. Industrial applications: Polyhale can be used in a variety of industrial applications, such as making glass, soap, and paper. Polyhalite crystal structure

References

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