Transmitted Light
Moderate pleochroism from colorless to yellow (pale to intense) to golden. Monoclinic, pseudo-orthorhombic. Distinct cleavage, high relief. May have many inclusions (“sieve texture”). Short prisms with pseudo-hexagonal sections. In XPL, colors up to 1st order orange. ES(+), B(+), 2V from 80-90º. Both images in PPL, rotated 90 degrees.
Strong pleochroism in various shades of yellow and brown to greenish. Triclinic. Medium-high relief, 1 perfect cleavage. Lamellae, fibers and needles. In XPL, intense 2nd to 4th order colors. Paralell extinction. B(-) with 2V from 0º (pseudo-uniaxial) to 30º. Looks like biotite, but has no mottled extinction. Both images in PPL, rotated 90 degrees.
Weak to strong pleochroism in yellow, usually brownish and reddish (orange or green possible). Tetragonal. Very high relief, cleavage not visible. In XPL, the color is almost the same as in PPL. Extinction tends to parallel, ES(+). Twins are common. U(+), anomalous 2V up to 38º. Both images in PPL, rotated 90 degrees.
Strongly pleochroic in orange (may be pink, yellow, red or violet). Rare. Monoclinic. High to extremely high relief, 1 perfect cleavage. Long prisms, sections with 6 sides. In XPL, intense colors, masked by the red color of the mineral. 0-34º or parallel extinction. ES(+/-), B(+/-). Both images in PPL.
Moderate brown pleochroism in sections perpendicular to (001); sections parallel to (001) almost without pleochroism. Monoclinic. It is a variety of biotite with lamellar habit, moderate relief, parallel and mottled extinction, ES(+) and B(-) with small 2V angle. Of marbles and basic igneous rocks.Both images in PPL, rotated 90 degrees.
Strong orange colors, can be red-brown. Pleochroism of variable intensity. It forms spherulites or radiated fibrous aggregates. The structure resembles that of chalcedony. In CPL, the color is almost the same. It has high birefringence and parallel extinction.
Amphibole with strong pleochroism between deep brown and reddish brown. Monoclinic. Basal sections with 2 cleavages at 56º and 124º. Moderate to high relief. Extinction 0-19º. In CPL, intense 1st to 2nd order colors, frequent zoning, B(-). Similar to biotite, but without mottled extinction. Both images in PPL, rotated 90 degrees.
APATITE: usually colorless, but may appear brownish to blue-gray and orange.
