Source : Webster's Revised Unabridged Dictionary (1913)

Stibnite \Stib"nite\, n. (Min.)
   A mineral of a lead-gray color and brilliant metallic luster,
   occurring in prismatic crystals; sulphide of antimony; --
   called also {antimony glance}, and {gray antimony}.

Source : WordNet®

stibnite
     n : a soft gray mineral; the chief ore of antimony