Transmitted Light
Strongly pleochroic in brown (may be in green, yellow, reddish, yellow or red). Monoclinic. Moderate relief. One perfect cleavage if not altered. In XPL, 3rd-4th order colors, masked by the strong mineral color. Paralell and mottled extinction. ES(+). Very common, alters to chlorite, which is green in PPL. Both images in PPL.
Weak pleochroism in brown, may have gray or yellow tones. The color usually is almost the same in PPL and in XPL. Granular or with rhombic basal sections. Monoclinic. High relief. Many fractures, 1 good cleavage, often absent. Twins and zoning possible. B(+), 2V=17-56°. Very common mineral. Both images in PPL.
Suggests pleochroism, but does not have. Typical of volcanic rocks. Strong brown color, rounded to polygonal shapes, high relief, without cleavage. In XPL, it is isotropic because it is a cubic mineral. It occurs together with brown hornblende and brown biotite! It is a black (Ti) variety of andradite garnet. Both images in PPL.
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 XPL, intense 1st to 2nd order colors, frequent zoning, B(-). Similar to biotite, but without mottled extinction. Both images in PPL.
It is an alteration of biotite or phlogopite. Pleochroic in pale shades of brown; may be colorless. Monoclinic. Low to medium relief, perfect cleavage, typical micaceous habit. In XPL, colors until the end of the 1st order. Extinction tends to parallel, but is not mottled! SE(+), B(-), 2V from 0 to 15º. Both images in PPL.
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.
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.
Pleochroic in yellow-brown, brown, greenish and colorless. Zoning is common. Monoclinic. High relief, cleavage is not visible. Anhedral or tabular grains. In XPL, colors up to 3rd order, masked by the mineral color. Pleochroic halos are possible, may be metamict (almost isotropic). Twins common, B(-/+).
Weak to strong pleochroism in brownish and reddish (may be orange or green). Tetragonal. Very high relief, cleavage not visible. In XPL, its own color masks the interference colors. Extinction tends to parallel. ES(+), twins are common. U(+), can have anomalous 2V up to 38º. Both images in PPL.
Weak pleochroism in red-brown or yellow-brown. Very high relief, granular or acicular crystals. Tetragonal. The color is almost the same in PPL and in CPL (similar to titanite). Parallel extinction, ES(+), twins possible. No zonation, no alteration, dark halos (radioactivity) possible. U(+). Both images in PPL.
Strong pleochroism in brown (yellow, blue, red, black and green possible). Trigonal. High relief, cleavage not visible, fractures perpendicular to elongation. Basal sections (without pleochroism) triangular or pseudo-hexagonal. Paralell extinction, ES(-), frequent zonation. U(-), can have 2V of 5º. Both images in PPL.
amphiboles with strong pleochroism in green colors, may be brownish. Monoclinic, basal sections with 2 cleavages at 56º-124º (pseudo-hexagonal!). Short to long prismatic, medium-high relief. In CPL, colors from upper 1st to lower 2nd order. Oblique extinction (14-22º), ES(+), Twins and zoning are common. B(-), 2V=34-90º. Both images in PPL.
Weak pleochroism in brown if not colorless. Tetragonal. High relief, cleavage not visible, roundish grains, may have a dark halo around it. In CPL, 3rd to 4th order colors. Frequent zoning. Paralell extinction , ES(+), rare twins. U(+), 2V of 10º is possible. Similar to monazite!
Moderate pleochroism in brown colors in various shades (including blue), when rich in Fe. Amphibole of medium to high grade metamorphic rocks. Typically asbestiform (fibrous) habit. Orthorhombic. Moderate relief, parallel extinction, ES(+). No twins nor zoning. B(+/-), 2V = 57 – 80 degrees.
Weak pleochroism in pale brown or pale green, stronger when Fe-rich. Medium-high relief. Amphibole. Monoclinic, occurs in parallel prismatic to fibrous crystals. In CPL, intense colors. Oblique extinction, ES(+), twins common, B(+/-).Very similar to other amphiboles!
