Linked from
The 27 pages that link to Gypsum, each with the reason it gives.
Mohs scaleBroader topic: It is the next standard mineral above talc.
EvaporiteBroader topic: Gypsum commonly precipitates early in the sequence of evaporite minerals.
SulfateBroader topic: It is a widespread sulfate mineral used in plaster and drywall.
Crystal waterBroader topic: Its crystal water distinguishes gypsum from anhydrous calcium sulfate.