pleochroism /plɪˈɒkrəʊˌɪzəm/

• 1. 

  N a property of certain crystals of absorbing light to an extent that depends on the orientation of the electric vector of the light with respect to the optic axes of the crystal. The effect occurs in uniaxial crystals (dichroism) and esp in biaxial crystals (trichroism) 多向色性