(n) a white or reddish mineral consisting of hydrous chlorides of potassium and magnesium; used as a fertilizer and as a source of potassium and magnesium
The Collaborative International Dictionary of English (GCIDE) v.0.53 Collaborative International Dictionary (GCIDE)
n. [ G. carnallit, fr. Von Carnall, a Prussian. ] (Min.) A hydrous chloride of potassium and magnesium, sometimes found associated with deposits of rock salt. [ 1913 Webster ]