syngenite

from The Century Dictionary.

• noun A hydrous sulphate of calcium and potassium, occurring in monoclinic crystals which are colorless or milky-white. It is found in cavities in rock-salt at Kalusz in Galicia, Austria-Hungary. Also called kaluszite.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun mineralogy a saline evaporite, consisting of a mixed potassium and calcium sulphate