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Important minerals
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Plagioclase
colorless, 2 cleavage planes 90, low relief, no pleochroism, inclined extinction, polytheistic twinning, and igneous and metamorphic
Olivine
colorless pink or green, no cleavage, 3rd order interference colors, high relief, 90 extinction angles, no pleochromism, no twinning,
Orthopyroxene
colorless pink—>green, 2 planes of cleavage, moderate to high relief, weak pleochromism, 1st order birefringence with parallel extinction, and fine twinning
Hornblende
Green/brown, 2 planes of cleavage at 60/120, high relief, strong pleochromism, 2nd order birefringence, and inclined extinction
Garnet
colorless, no cleavage, high relief, no pleochromism, isotropic, no extinction angle, no twinning, often metamorphic.
Sillimanite
Colorless,1 cleavage plane, high relief, no pleochromism, 1st-2nd orderbirefringence, parallel extinction, no twinning, metamorphic
Clinopyroxene
Colorless to light brown/green, 2+ cleavage planes at 90 degrees, Moderate to high relief, weak pleochroism, 2nd order birefringence, inclined extinction, sometimes twinning
Quartz
Colorless, No cleavage, Low relief, no pleochroism, 1st order birefringence, undulatory extinction type, no twinning, metamorphic
K-Feldspar
Colorless, 2 planes @ 90 degrees, low relief, no pleochroism, 1st order Birefringence, parallel extinction, carlsbad twinning
Chlorite
Green/blue to pale, Basal cleavage - 1 plane, low to moderate relief, Pleochroism, 1st order birefringence, parallel extinction, metamorphic
Staurolite
colorless to yellow, no cleavage, high relief, strong pleochroism, 1st Order, parallel extinction, no twinning, and metamorphic
Muscovite
colorless to weak, 1 basal cleavage plane, no pleochroism, low relief, 2nd-3rd order birefringence, parallel extinction, and fine twinning.
Kyanite
colorless to weak, 2 planes of cleavage at 75-80 degrees, high relief, weak pleochroism, 1st order birefringence, inclined extinction, has twinning, and is metamorphic
Biotite
brown/green to reddish brown with 1 basal cleavage plane, strong pleochroism, low to moderate relief, 2nd-3rd order birefringence, and fine twinning. It also has bird’s eye extinction.
Calcite
Colorless or white mineral with 3 cleavage planes, high relief, no pleochromism, 4th order birefringence, and has symmetrical extinction, and twinning