Syngenite is an uncommon potassium calcium sulfate mineral with formula K2Ca(SO4)2·H2O.

It was first described in 1872 for an occurrence as druse on halite in the Kalusa Salt deposit, Ivanovo-Frankovsk Oblast', Ukraine.

It also forms as a volcanic sublimate, as vein fillings in geothermal fields and in caves where it is derived from bat guano.

It occurs in association with halite and arcanite in salt deposits; and with biphosphammite, aphthitalite, monetite, whitlockite, uricite, brushite and gypsum in cave environments.

[5] Syngenite can be artificially produced by the action of a potassium sulfate solution on gypsum.