{{infobox mineral | name = Pickeringite | boxwidth = | boxbgcolor = | image = Pickeringite-87353.jpg | imagesize = | alt = | caption = Cobalt rich pickeringite from the Northern Slanské Mts, Prešov Region, Slovakia | category = Sulfate mineral | formula = MgAl<sub>2</sub>(SO<sub>4</sub>)<sub>4</sub>·22(H<sub>2</sub>O) | IMAsymbol = Pkg<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3 |pages=291–320|doi=10.1180/mgm.2021.43 |bibcode=2021MinM...85..291W |s2cid=235729616 |doi-access=free}}</ref> | molweight = | strunz = 7.CB.85 | dana = | system = Monoclinic | class = Prismatic (2/m) <br/><small>(same H-M symbol)</small> | symmetry = ''P''2<sub>1</sub>/c | unit cell = a = 20.8, b = 24.2, <br/>c = 6.18 [Å]; β = 95°; Z = 4 | color = Colorless, white; may be shades of yellow, green, or red due to impurities | colour = | habit = Rarely as acicular crystals, radial or matted aggregates; typically as incrustations and efflorescences | twinning = | cleavage = Poor on {010} | fracture = Conchoidal | tenacity = | mohs = 1.5 | luster = Vitreous | streak = | diaphaneity = Semitransparent | gravity = 1.73–1.79 | density = | polish = | opticalprop = Biaxial (−) | refractive = n<sub>α</sub> = 1.476 n<sub>β</sub> = 1.480 n<sub>γ</sub> = 1.483 | birefringence = δ = 0.007 | pleochroism = | 2V = Measured: 60° | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = Completely soluble in water | impurities = May contain iron, manganese or cobalt | alteration = | other = | prop1 = | prop1text = | references = <ref name=HBM>[http://rruff.info/doclib/hom/pickeringite.pdf Handbook of Mineralogy]</ref><ref name=Mindat>[http://www.mindat.org/min-3204.html Pickeringite on Mindat.org]</ref><ref name=Webmin>[http://www.webmineral.com/data/Pickeringite.shtml Pickeringite data on Webmineral]</ref><ref>[https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Pickeringite Mineralienatlas]</ref> }}
'''Pickeringite''' is a magnesium aluminium sulfate mineral with formula MgAl<sub>2</sub>(SO<sub>4</sub>)<sub>4</sub>·22(H<sub>2</sub>O). It forms a series with halotrichite.
It forms as an alteration product of pyrite in aluminium rich rocks and in coal seams. It also occurs in pyrite rich hydrothermal ore deposits in arid regions. It forms in fumaroles and in caves. It occurs with kalinite, alunogen, epsomite, melanterite, copiapite and gypsum.<ref name=HBM/>
It was first described in 1844 as reflective for an occurrence in Cerros Pintados, Pampa del Tamarugal, Iquique Province, Tarapacá Region, Chile. It was named for American linguist and philologist John Pickering (1777–1846).<ref name=Mindat/> thumb|upright|left|Pickeringite in the Natural History Museum
==References== {{reflist}}
Category:Sulfate minerals Category:Monoclinic minerals Category:Minerals in space group 14 {{sulfate-mineral-stub}}