i. The property by which some doubly refracting crystals absorb the ordinary rays (O-rays) completely and extraordinary rays whose direction is parallel to the optic axis passing through the crystal, is called dichroism.
ii. The crystal possessing dichroism property is called dichroic crystal.
iii. Dichroic substance produces linearly polarised light.
iv. This property of substance is used to construct a polaroid.
Example: Tourmaline crystal.