Source : Webster's Revised Unabridged Dictionary (1913)

Periclase \Per"i*clase\, Periclasite \Per`i*cla"site\, n. [Pref.
   peri- + Gr. ? to break.] (Min.)
   A grayish or dark green mineral, consisting essentially of
   magnesia (magnesium oxide), occurring in granular forms or in
   isometric crystals.

Source : WordNet®

periclase
     n : a white solid mineral that occurs naturally as periclase; a
         source of magnesium [syn: {magnesia}, {magnesium oxide}]