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Polyhalite

Sedimentary mineral

Field	Value
name	Polyhalite
image	History museum of Truskavets 081.jpg
caption	Museum specimen of polyhalite and anhydrite
category	Sulfate mineral
formula
IMAsymbol	Plhl
strunz	7.CC.65
system	Triclinic
class	Pinacoidal ()
(same H-M symbol)
symmetry	F
unit cell	a = 6.95 Å, b = 8.88 Å,
c = 6.95 Å; α = 104.06°,
β = 113.94°, γ = 101.15°; Z = 4
color	Colorless, white, gray; often salmon-pink to brick-red from included iron oxide
habit	Typically fibrous, foliated, massive; rarely as tabular crystals; pseudo-orthorhombic
twinning	Characteristically polysynthetic on {010}, {100}
cleavage	Perfect on {10}; parting on {010}
fracture	Conchoidal
tenacity	Brittle
mohs	3.5
luster	Vitreous to resinous
streak	White
diaphaneity	Transparent
gravity	2.78
opticalprop	Biaxial (−)
refractive	nα = 1.546 – 1.548 nβ = 1.558 – 1.562 nγ = 1.567
birefringence	δ = 0.021
2V	Measured: 60° to 62°
solubility	Soluble in water, with precipitation of gypsum and perhaps syngenite
references

(same H-M symbol) c = 6.95 Å; α = 104.06°, β = 113.94°, γ = 101.15°; Z = 4 | length fast/slow = 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 iron oxide inclusions. It has a Mohs hardness of 3.5 and a specific gravity of 2.8. It is used as a valuable fertilizer.

Polyhalite was first described in 1818 for specimens from its type locality in Salzburg, Austria. It occurs in sedimentary marine evaporites and is a major potassium ore mineral in the Carlsbad deposits of New Mexico. It is also present as a 2–3% contaminant of Himalayan salt. The only deposit currently being mined lies under North Yorkshire, UK, extending under the adjacent North Sea.

Name

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.

Extraction

The only polyhalite mined in the world comes from a layer of rock over 1000 m below North Yorkshire and extending off the North Sea coast in the UK, deposited 260 million years ago.

In 2010, the first mining operations of this polyhalite mineral layer commenced at Boulby Mine, and the mine is in 2023 the only producer of polyhalite, marketed by ICL Group Ltd. as Polysulphate. 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 and construction of two 1500 m shafts to reach the 70 m mineral seam was underway in 2015. These will reach a mineable area of around 25200 ha and Woodsmith Mine will be the deepest in Europe. The Woodsmith project was originally slated to begin production in 2027; development has since been slowed, and Anglo American now expects to ramp up construction from 2027, with a new first production date yet to be announced.

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.

References

Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
[http://www.mindat.org/min-3259.html Polyhalite on Mindat.org]
[http://webmineral.com/data/Polyhalite.shtml Polyhalite data on Webmin]
[http://rruff.info/doclib/hom/polyhalite.pdf Handbook of Mineralogy]
"POLYHALITE {{!".
(1 September 2016). "Banks backstop Sirius Minerals for $2.9B UK potash mine".
"North York Moors potash mine gets £1.7bn go-ahead". The Guardian. 30 June 2015. Retrieved 3 February 2016.
GeoResources. "Anglo American’s Woodsmith Mine expected to ‘ramp up’ from 2027". 2024. Accessed 14 January 2026. https://www.georesources.net/cms.php/en/news/2502/Anglo-American-s-Woodsmith-Mine-expected-to-ramp-up-from-2027
New Ag International. "Anglo American eyeing final investment decision on UK polyhalite project by 2027". 2024. Accessed 14 January 2026. https://www.newaginternational.com/specialty-fertilizer/anglo-american-eyeing-final-investment-decision-on-uk-polyhalite-project-by-2027/
The Guardian. "Anglo American takes further £1bn writedown on Yorkshire fertiliser mine". 25 July 2024. Accessed 14 January 2026. https://www.theguardian.com/business/article/2024/jul/25/anglo-american-takes-further-1bn-writedown-on-yorkshire-fertiliser-mine

Info: Wikipedia Source

This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.

magnesium-minerals calcium-minerals potassium-minerals sulfate-minerals triclinic-minerals evaporite potash minerals-in-space-group-2

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