Aluminite is a hydrous aluminium sulfate mineral with formula: Al2SO4(OH)4·7H2O. It is an earthy white to gray-white monoclinic mineral which almost never exhibits crystal form. It forms botryoidal to mammillary clay -like masses. It has a very soft Mohs hardness of 1–2 and a specific gravity of 1.66–1.82.
It forms in clay deposits as an oxidation along with aluminium silicates. It also occurs in volcanic sublimates deposits and rarely in caves , gibbsite , celestine and goethite
It was first described in 1807 from Halle , Saxony-Anhalt and named for its aluminium content. It is also known as alley stone, halite and websterite (named after Orcadian geologist Thomas Webster).
Aluminite is used by tile and masonry workers to reduce the setting time of mortars.