Source : Webster's Revised Unabridged Dictionary (1913)

Realgar \Re*al"gar\, n. [F. r['e]algar, Sp. rejalgar, Ar. rahj
   al gh[=a]r powder of the mine.] (Min.)
   Arsenic sulphide, a mineral of a brilliant red color; red
   orpiment. It is also an artificial product.

Source : WordNet®

realgar
     n : a rare soft orange mineral consisting of arsenic sulphide;
         an important ore of arsenic