marcasite [m??r???k?? s??t???]Use marcasite in a sentence noun an orthorhombic mineral, FeS, that is dimorphic with pyrite; iron sulfide this mineral cut and mounted on silver or other white metal to look like brilliantsOrigin of marcasiteFrench marcassite ; from Medieval Latin marcasita ; from Arabic marqash??t?? ; from Persian marqash??sh??