The Collaborative International Dictionary of English v.0.48:

Polyhalite \Pol`y*ha"lite\, n. [Poly- + Gr. ? salt.] (Min.)
   A mineral usually occurring in fibrous masses, of a brick-red
   color, being tinged with iron, and consisting chiefly of the
   sulphates of lime, magnesia, and soda.
   [1913 Webster] Polyhedral