Reflected Light
PPL: light gray to bluish gray to cream color, with very strong pleochroism. Reflectivity of 20-44%, with high bireflectance. Typical lamellar habit; the lamellae may be deformed.
XPL: extreme anisotropy between brown, bluish and turquoise at XPL+2º. No internal reflections. Graphite is similar, but at XPL+2° the color of graphite is straw yellow. Polishing scratches are possible.
Images: in XPL, molybdenite (bluish), gangue (milky).
PPL: Medium to dark gray color with a brown tinge. Very strong pleochroism in gray. Variable reflectivity from 7 to 21%, with very strong bireflectance. Typical lamellar habit, such as molybdenite.
XPL: extreme anisotropy between light brown gray and dark gray. Uncrossing the nicols two degrees, one of the colors is straw yellow. No internal reflections. Molybdenite: anisotropy with a bluish tinge.
Images: in XPL+2º, graphite (yellowish), mica (dark), quartz (light).
PPL: medium gray color. Reflectivity from 10 to 31%. Weak pleochroism and bireflectance, difficult to see. Radiated acicular crystals or in bands. Difficult identification. Very similar to other manganese minerals.
XPL: strong anisotropy in gray colors with brown tones. No internal reflections. In small crystals, the anisotropy is barely visible.
Images: in XPL+2º, hollandite in radiated aggregate of fine crystals.
PPL: medium to dark gray color. Reflect 26-31%. Pleochroism and clear bireflectance. Fibrous crystals in porous aggregates.
XPL: strong anisotropy from gray-brown to dark and to blue. Alteration of primary Mn minerals. Also in polymetallic nodules.
PPL: medium gray color. Reflectivity from 10 to 16%. Distinct pleochroism. Strong bireflectance, hard to see when crystals are thin.
XPL: very strong anisotropy in bluish gray tones. Sparse rare red internal reflections. Typical as alteration of iron ores.
Images: in XPL, lepidocropcite with strong anisotropy in blue and gray and some internal reflections.
