306 PHYSIOGRAPHY. CLASS n. 



varieties are not known, having been found only in the 

 alluvial deposits of rivers along with other species of 

 gems. Thus it occurs in Brazil, along with octahedral Dia- 

 mond and prismatic Topaz ; also in Ceylon. Near Had- 

 dam in Connecticut and Saratoga in New York, it occurs 

 in a kind of granite, imbedded in Albite and rhombohedral 

 Quartz, and associated with dodeeahedral Garnet, rhombo- 

 hedral Emerald, rhombohedral Tourmaline, and prismatic 

 Tantalum-ore. The original matrix of the large Siberian 

 crystals is not known. 



GENUS III. DIAMOND. 

 1. OCTAHEDRAL DIAMOND. 



Octahedral or Common Diamond. JAM. Syst. Vol. I. p. 

 1. Octahedral Diamond. Man. p. 187. Diamond. 

 PHILL. p. 361. Demant. WERN. Hoffm. H. B. I. S. 

 358. Demant. HAUSM. I. S. 59. Diamant. LEONH. 

 S. 115. Diamant. HAUY. Traite, T. III. p. 287. 

 Tabl. comp. p. 60. Traite', 2de Ed. T. IV. p. 419. 



Fundamental form. Hexahedron. Vol. 1. Fig. 1. 



Simple forms. H ; 6. Vol. I. Fig. 2. ; D. Vol. I. 

 Fig. 81. ; T. Vol. I. Fig. 35. 



Char of Comb. Tessular. 



Combinations. 1. H. D. Fig. 151. 2. O. D. 



3. O. T. 4. O. D. T. All of them from Brazil. 



Irregular forms, grains. 



Cleavage, octahedron, highly perfect. Fracture 

 conchoidal. Surface, the octahedron sometimes 

 faintly streaked parallel to its edges of combina- 

 tion, but in general very smooth. Also the do- 

 decahedron if often streaked, rough, and uneven, 

 the tetraconta-octahedron curved, and smooth. 

 Grains possess a rough and granulated surface. 



