Source : Webster's Revised Unabridged Dictionary (1913)

Kainite \Kai"nite\, n. [Gr. ? recent.] (Min.)
   A compound salt consisting chiefly of potassium chloride and
   magnesium sulphate, occurring at the Stassfurt salt mines in
   Prussian Saxony.

Source : WordNet®

kainite
     n : a white mineral consisting of magnesium sulphate and
         potassium chloride; a source of potassium salts; used as
         a fertilizer