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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.