In this paper the author commences with a summary of the present state of knowledge as to the internal constitution of crystalline bodies; and he then proceeds to describe the optical figures produced by the disintegrated surfaces of minerals and artificial minerals, according as the disintegration is effected—1. By the action of solvents while the crystal is forming, or remains in the bowels of the earth; 2. By the action of solvents on the surface of perfect crystals; and 3. By mechanical abrasion.