a white or colorless mineral, KCl, that is the chief ore of the potassium used to make fertilizers
See sylvite in American Heritage Dictionary 4
syl·vite
noun
A colorless vitreous potassium chloride mineral, the major ore of potassium.
Origin: Alteration of sylvine, from French, from New Latin (sal digestivus) Sylvii, (digestive salt) of Sylvius, probably after Franz de la Boë, or Franciscus Sylvius (1614-1672), German-born Dutch physician.