ORDER VII. RHOMBOHEDllAL EMERALD. 317 



sometimes rough, sometimes having a very flat 

 six-sided pyramid upon it, the terminal edges of 

 which are about 179 40'. 



Lustre vitreous. Colour green, passing into blue, 

 yellow, and white ; the brightest of these colours 

 is emerald-green, the greater part of the others 

 is pale. Streak white. Transparent ... trans- 

 lucent. 



Hardness = 7-5 . . . 8-0. Sp. Gr. = 2-732 of a per- 

 fectly emerald-green variety ; 2-678, apple- 

 green beryl. 



Compound Varieties. Massive : composition ge- 

 nerally large granular, sometimes imperfectly co- 

 1 umnar. 



OBSERVATIONS. 



1. The only remarkable differences between Emerald and 

 Beryl are in their colours, which, however, produce such 

 an uninterrupted series, that only arbitrary limits can be 

 fixed within it. The colour of Emerald is emerald-green ; 

 all the varieties of other colours are Beryl. The division 

 of the latter into precious and common Beryl depends upon 

 the more or less perfect formation of the varieties concern- 

 ed, particularly in regard to pureness and transparency. 

 By divisions of this kind, however, the species becomes 

 less interesting than it otherwise would be, on account of 

 the great number of different varieties which it contains. 



2. The analysis of a variety of Beryl from Broddbo 

 has yielded to BERZELIUS, and that of a variety of Eme- 

 rald from Peru to KLAPROTH, 



Silica 68-35 68-50. 



Alumina 17'60 15-75. 



Gluclna 13-13 12-50. 



Ox de of Iron 0-72 1-00. 



