4 DIAMOND FAMILY. 16. Octahedron, in which each of the planes is divided | . into three compartments; the dividing edges run ning from the middle point of the plane to the angles. | 17. Octahedron, in which the edges are bevelled, and | the bevelment once broken. j 18. Octahedron, in which each of the planes is divided I ' into six compartments; three of the dividing i edges run from the middle of the plane to the i middle of the edges; and three to the angles of : the octahedron. Plate I. fig. 2. ‘ 19. Six-sided table, with oblique terminal planes *. ! The crystals are small, and seldom middle-sized : they occur loose and single; rarely two or three are irregular - ly aggregated together. I The surface of the octahedrons is smooth or streaked; that of the grains uneven, granulated, sometimes ap proaching to drusy, and frequently rough. ■ Externally, its lustre alternates from splendent to glim mering ; internally, it is always splendent, often specu lar-splendent, and the lustre is adamantine. | The fracture is straight and periect foliated, with a fourfold equiangular cleavage; and the cleavages are pa rallel with the sides of the octahedron. The fragments are octahedral or tetrahedral. ; It rarely occurs in distinct concretions; and these are ^ small, and fine granular. It is seldom completely transparent; more generally it rather * Some authors mention the cube as one of the forms of the diamond : Weiss assures us he saw a cubic diamond in the King of Prussia's collection in Berlin, and Mr Koenig of the British Mu. enm inf rms me, that Mr jfcowry hag in his collection a cubic diamond, truncuted on its edges.
