Source : Webster's Revised Unabridged Dictionary (1913)

Carnallite \Car"nal*lite\, n. [G. carnallit, fr. Von Carnall, a
   Prussian.] (Min.)
   A hydrous chloride of potassium and magnesium, sometimes
   found associated with deposits of rock salt.

Source : WordNet®

carnallite
     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