From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
Cobalt rich pickeringite from the Northern Slanské Mts, Prešov Region, Slovakia
CategorySulfate mineral
(repeating unit)
IMA symbolPkg[1]
Strunz classification7.CB.85
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/c
Unit cella = 20.8, b = 24.2,
c = 6.18 [Å]; β = 95°; Z = 4
ColorColorless, white; may be shades of yellow, green, or red due to impurities
Crystal habitRarely as acicular crystals, radial or matted aggregates; typically as incrustations and efflorescences
CleavagePoor on {010}
Mohs scale hardness1.5
Specific gravity1.73–1.79
Optical propertiesBiaxial (-)
Refractive indexnα = 1.476 nβ = 1.480 nγ = 1.483
Birefringenceδ = 0.007
2V angleMeasured: 60°
SolubilityCompletely soluble in water
Common impuritiesMay contain iron, manganese or cobalt

Pickeringite is a magnesium aluminium sulfate mineral with formula MgAl2(SO4)4·22(H2O). 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.[2]

It was first described in 1844 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).[3]

Pickeringite in the Natural History Museum


  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85: 291–320.
  2. ^ a b Handbook of Mineralogy
  3. ^ a b Pickeringite on Mindat.org
  4. ^ Pickeringite data on Webmineral
  5. ^ Mineralienatlas