Polyhalite is an

evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocean ...

mineral, a hydrated

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...

potassium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...

and

magnesium Magnesium is a chemical element with the 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 of the periodic ...

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 Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of wh ...

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 various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by ...

of 3.5 and a

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its dens ...

of 2.8. It occurs in sedimentary marine evaporites and is a major potassium ore mineral in the Carlsbad deposits of

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...

. 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 Salzburg (, ; literally "Salt-Castle"; bar, Soizbuag, label=Austro-Bavarian) is the fourth-largest city in Austria. In 2020, it had a population of 156,872. The town is on the site of the Roman settlement of ''Iuvavum''. Salzburg was founded ...

, Austria. 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 ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...

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 Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...

'' (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 chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively c ...

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

off the

North Yorkshire North Yorkshire is the largest ceremonial county (lieutenancy area) in England, covering an area of . Around 40% of the county is covered by national parks, including most of the Yorkshire Dales and the North York Moors. It is one of four co ...

coast in the UK. Deposited 260 million years ago, it lies below the

potash Potash () includes various mined and manufactured salts that contain potassium in water- soluble form.

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 Anglo American plc is a British listed 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 diamonds, copper ...

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