Source : Webster's Revised Unabridged Dictionary (1913)

Plagioclase \Pla"gi*o*clase\, n. [Gr. ? oblique + ? to break.]
   (Min.)
   A general term used of any triclinic feldspar. See the Note
   under {Feldspar}.

Source : WordNet®

plagioclase
     n : any of a rock-forming series of triclinic feldspars [syn: {oligoclase}]