Carnallite

Carnallite, a hydrous potassium and magnesium chloride found in considerable quantity at Stassfurt in Prussian Saxony, associated with rock salt and with other potassium salts, and named after Herr von Carnall, director of the mines, who first called attention to its value as a source of potassium, for which it is now largely worked. It generally occurs massive and reddened from the presence of iron-oxide, breaks conchoidally, deliquesces and phosphoresces.