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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Sajan sarthak
There are following types of extinction seen in minerals 1.parallel where the vibration direction of minerals coincides with the vibration direction of crossed nicols and it's parallel to cleavage of mineral. 2.Inclined extinction where the vibration direction and cleavage are at angle to each other . 3.Symmetrical extinction if the mineral cleavage direction exactly bisects the vibration direction. Olivine- straight Opx- parallel Cpx-inclined, 45⁰ Orthoamphibole- parallel Clinoamphibole- 10⁰ to 20⁰ Feldspar- 15⁰ to30⁰ Quartz - wavy extinction Mica- parallel Chlorite- parallel