Wiktionary
n. (context mineralogy English) A hydrous potassium uranium sulfate mineral with chemical formula K4(UO2)6(SO4)3(OH)10·4(H2O), forming yellow to reddish-brown monoclinic-prismatic crystals with perfect cleavage and formerly used in the manufacture of paint.
Wikipedia
Zippeite is a hydrous potassium uranium sulfate mineral with formula: K( U O)( SO)(O H)·4( HO). It forms yellow to reddish brown monoclinic-prismatic crystals with perfect cleavage. The typical form is as encrustations and pulverulent earthy masses. It forms as efflorescent encrustations in underground uranium mines. It has a Mohs hardness of 2 and a specific gravity of 3.66. It is strongly fluorescent yellow in UV radiation and is a radioactive mineral.