568 



DETERMINATION OP PRECIOUS STONES 



The two members of this group most likely to be confused are aquamarine and topaz, 

 since they are often identical in colour. There need be no confusion, however, since they 

 differ very widely in specific gravity, the latter falling into Division II. and the former into 

 Division IV. Euclase, a rare mineral of much the same colour, is distinguished by the same 

 feature, namely, the specific gravity. 



The distinctions between corundum ("oriental aquamarine"), diamond, and topaz have 

 been dealt with in the first table. 



The specific gravity, low degree of hai'dness, and single refraction unite to distinguish 

 fluor-spar from other stones of the same group ; it is always rather darker in colour than 

 are aquamarine, topaz, or euclase. Glass is singly refracting and much softer than any of 

 the stones included in this group except fluor-spar. 



3. PALE BLUE STONES. 



The remarks given under the first and second tables will enable the stones brought 

 together here to be distinguished ; those of more frequent occurrence are readily recognised 

 by the specific gravity alone. 



4. BLUE STONES. 



By far the most important of these is sapphire; the only other blue stones of 

 consequence as gems are spinel and tourmaline. The former is distinguished by the fact 

 that it is singly refracting, while sapphire and tourmaline differ widely in density. The 



