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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Gurmeet Singh posted an Question
February 03, 2021 • 06:23 am
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30 points
30 points
- IIT JAM
- Geology (GG)
Under crossed polars, a mineral remains dark at all stages of rotation of the microscope stage. which of the following statement(s) is/are not correct? (a) the
Under crossed polars, a mineral remains dark at all stages of rotation of the microscope stage. Which of the following statement(s) is/are NOT correct? (A) The mineral is isotropic. (B) The mineral is biaxial with an optic orientation corresponding to the principal section of the indicatrix. (C) The mineral is biaxial with an optic orientation containing the Y-vibration direction only. (D) The mineral is uniaxial with an orientation perpendicular to the optic axis.
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Asif ali Best Answer
A,C,D will be the condition to found a dark minerals under 360° rotation of microscopic stage under XPL. basically for example Garnet is an isotropic mineral and appears dark of 360° rotation and Biaxial mineral may be dark if found along Y direction if you cut a section along Y vibration direction of a biaxial mineral it appears dark because it shows X,Z direction vibration interference colours but not in Y direction as well as all you know about perpendicular to C axis which is optic axis of uniaxial minerals appears dark.