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

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 occurs with kalinite, alunogen, epsomite, melanterite, copiapite and gypsum.

[2] It was first described in 1844 as reflective for an occurrence in Cerros Pintados, Pampa del Tamarugal, Iquique Province, Tarapacá Region, Chile.