Reflected Light
PPL: white color with strong white (gray) to olive gray pleochroism. Reflectivity of 30-45%, with distinct bireflectance.
XPL: strong anisotropy between gray, brown and blue. No internal reflections. Parallel extinction. Prismatic habit. Twins are frequent.
Images: in XPL, stibnite with typical colors and twins.
PPL: light gray to bluish gray to cream color, with very strong pleochroism. Reflectivity of 20-44%, with high bireflectance. Typical lamellar habit (similar of micas), may be deformed.
XPL: extreme anisotropy between brown, bluish and turquoise at CPL+2º. No internal reflections. Graphite is similar, but at CPL+2 the color of graphite is straw yellow. Possible polishing scratches.
Images: in XPL, molybdenite lamellae with anisotropy.
PPL: medium to dark gray color with a brown tinge. Very strong pleochroism in gray. Variable reflectivity from 7-21%, with very strong bireflectance. Typical lamellar habit, such as molybdenite.
XPL: extreme anisotropy between light brown gray and dark gray. Uncrossing the nicols in 2o, one of the colors is straw yellow. No internal reflections. Molybdenite: anisotropy with a blue tint.
Images: in XPL+2º, graphite (yellowish), mica (dark), quartz (lighter).
Try to find it in the group of white minerals with weak to distinct pleochroism and/or bireflectance, with anisotropy in varying degrees in XPL (RL11).