Transmitted Light
In PPL colorless, rarely with pale colors. Monoclinic, with lamellar habit. Medium-high relief, usually one perfect cleavage. In XPL, intense colors up to 3rd order. ES(+), B(-), (2V=30-47º). Very common, but never occurs in volcanic rocks. Difficult to distinguish from talc, lepidolite, pyrophyllite and paragonite.
In PPL strongly pleochroic in brown, yellow-brown, or red-brown colors (rarely yellow or red). Monoclinic, medium relief. Shows one perfect cleavage (not in basal sections!). In XPL, strong and vivid 3rd and 4th order colors, masked by its own strong color. ES(+), B(-) (2V from 0 to 35°). Very common.
In PPL colorless. Very rare lithiniferous mica. Monoclinic, low relief (diagnostic!). One perfect cleavage. In XPL, intense colors up to 2nd order. ES(+), rare twins, no zonation. B(-), 2V from 0 to 43º, can simulate being uniaxial. Very similar to muscovite, whose relief is higher.
In PPL always colorless. Rare mineral. Low to moderate relief, perfect (001) cleavage. Monoclinic. Lamellar habit and others. In XPL, intense colors up to 3rd and 4th order. ES(+/-), never show twins or zonation. B(-), with 2V from 53 to 62 degrees. Very similar to muscovite and talc.
In PPL colorless with medium relief. Fibers, scales or dense aggregates. Monoclinic or triclinic. Can show perfect cleavage in one direction. In XPL, intense interference colors up to 3rd order. ES(+), B(-), 2V from 0 to 30º. Rare twins, no zonation. Very similar to muscovite, whose 2V < 30º!
In PPL colorless, but may have weak to strong pleochroism in pale colors (yellow, orange, pink) or reddish or brown. Monoclinic, moderate relief, perfect cleavage, lamellar habit, ES(+). B(-) with small 2V, can simulate to be uniaxial. It is classified in the biotite series and is very similar to it. Occurs in silica subsaturated volcanic rocks, marbles, skarns and carbonatites.
In PPL colorless, but may show pleochroism in pale brown, inherited from the biotite that gave rise to it. Monoclinic. Extinction can be a little bit mottled. Perfect (001) cleavage, also inherited from biotite. In XPL, gray, white, yellow orange to bluish colors. B(-) with small 2V.
In PPL always colorless. Rare mineral. Trigonal, lamellar habit, medium relief. Perfect {0001} cleavage. Weak interference colors, only up to the end of the 1st order. ES(-) (important!), U(+), may have anomalous 2V. Similar to muscovite, talc and pyrophyllite, occurs in marbles and serpentinites.
