ORDER VII. GENERA AND SPECIES. 431 



4. PRISMATIC. Prismatic. Pr = 119 48'. (p" + os) 3 



= 70 41'. 



Cleavage, ?r + os. Less distinct, Pr -f 93, 

 H. = 8-5. 

 G. =3-65 ...3-8. 



Clirysdberyl. ii. 304. 



IT I. DIAMOND. Tessular. . 

 H. = 10-0. 

 G. = 3-4 ... 3-6. 



1. OCTAHEDRAL. Tessular. 



Cleavage, octahedron, perfect. 



Diamond. ii. 306. 



IV. TOPAZ. Prismatic. 



Cleavage, axotomous. 



H. = 8-0. 



G. = 3-4 ... 3-6. 



1. PRISMATIC. Prismatic. P = 1417', 101 52', 90 55'. 



P + os = 124 19'. 

 Combinations sometimes different in the opposite ends 



of the crystals. 

 Cleavage, P os, highly perfect. 



Topaz. ii. 308, 



V. EMERALD. Rhombohedral, prismatic. 



Cleavage, rhombohedral axotomous and 

 peritomous, or prismatoidal of a high 

 degree of perfection. 



H. = 7-5 ... 8-0. 



G. = 2-6 ...3-2. 



