Pickeringite is a magnesium 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, epsomite and gypsum
It was first described in 1844 for an occurrence in Cerros Pintados, Pampa del Tamarugal , Tarapacá Region. It was named for American linguist and philologist John Pickering (1777–1846).