The diamond belongs to the isometric system of crystallography ; the prevailing form is octahedral. It frequently occurs with curved faces and edges. Twin crystals (macles) are not uncommon. Diamond crystals are. generally perfect on all sides. They seldom show irregular sides or faces by which they were attached to a support, as do artificial crystals of chemical salts ; another proof that the diamond must have crystallised from a dense liquid.
The accompanying illustration (Fig. 14) shows some of the various crystalline forms of native diamonds.
No. 1. Diamond in the form of a hexakisoctahedron (the forty-eight scalenohedron), or a solid figure contained by forty-eight scalene triangles. According to Professor Maskelyne, this occurs as a self-existent form only in the diamond.
No. 2. Diamond in the form of a hexakis86