pléochroïque

CONT: Les absorptions des deux rayons, ordinaire et extraordinaire, peuvent être différentes; le minéral est dit alors «pléochroïque». Lorsqu'on fait la platine du microscope en lumière naturelle, la couleur ne varie pas, mais en lumière polarisée non analysée elle est différente suivant les orientations.

CONT: Pleochroic minerals are minerals that show different colors depending on what direction the viewer is observing the crystal. ... The greatest [color] change is limited to three colors and is called trichroic. A two color change is called dichroic. Pleochroic, which means ""many colors,"" is often the term used to cover both.
CONT: Pleochroic colors are observed and recorded in the mineral data and are generally diagnostic of the particular mineral.