pickeringite

{{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 = MgAl2(SO4)4·22(H2O) | IMAsymbol = Pkg | molweight = | strunz = 7.CB.85 | dana = | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = P21/c | unit cell = a = 20.8, b = 24.2, 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 = nα = 1.476 nβ = 1.480 nγ = 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 = }}

Pickeringite is a magnesium aluminium sulfate mineral with formula MgAl2(SO4)4·22(H2O). It forms a series with halotrichite.