What are sulphates in mineralogy ?

Sulphates : definition

Sulphates constitute the main subclass of the mineralogical class of "sulphates, chromates, molybdates, tungstates", strong of more than 300 species.

The sulphate subclass is characterized by the presence of the radical (SO4)2-, a fundamental structural element to which one or more cations are associated. The structure is balanced by the presence of large divalent cations : Ca2+, Mg2+, Fe2+, Ba2+, etc...

It contains around 270 minerals, divided into hydrated sulphates (including gypsum CaSO4 2H2O) and anhydrous sulphates (baryte BaSO4, celestite SrSO4, etc...).
Gypsum from Naica, Mexico
Celestite from Madagascar
Baryte from Châtel-Guyon, Puy-de-Dôme, France