574 



DETERMINATION OF PRECIOUS STONES 



The commonest stones of a yellow colour are citrine, topaz, and the yellow variety 

 of corundum known as "oriental topaz," they are easily distinguished from each othe^y 

 the differences in their specific gravity. Several other stones of this group are not altogether 

 uncommon in the precious stone market. 



The colour of hyacinth is never pure yellow, but is always definitely inclined to red, 

 while the yellow of chrysoberyl and chrysolite has always a greenish tinge. In stones of not 

 too small size, " oriental topaz " may be recognised by an exact determination of the 

 specific gravity. Hyacinth is not capable of scratching topaz, but this latter is scratched 

 both by " oriental topaz " and by chrysoberyl : and " oriental topaz " will scratch chrysoberyl, 

 a specimen of which may be conveniently kept for this test. 



Topaz, diamond, and chrysolite are distinguished from each other by differences in 

 hardness and in their behaviour in the polariscope, while the specific gravity is in each case 

 sufficient to distinguish them from the stones included in other divisions. Topaz and 

 citrine differ both in specific gravity and in hardness ; the former sinks in pure methylene 

 iodide, and, moreover, is capable of scratching quartz. 



Although beryl and citrine fall into different divisions of this group, there is very 

 little difference in their specific gravities, and in some cases there may be uncertainty 

 as to the identity of these stones. Beryl, nevertheless, is always rather heavier than 

 citrine (quartz), and sinks in liquid No. 4, in which citrine remains suspended. It is also 

 characterised by its capability of scratching quartz, which, of course, is not possessed by 

 citrine. Beryl is both lighter and harder than chrysolite. 



Amber, fire-opal, and glass are distinguished in the manner already explained in the 

 remarks appended to preceding tables. 



13. YELLOWISH-GREEN STONES, 



Of the stones included in the first division of this group, chrysoberyl is most frequently 

 met with : it is chai-acterised by great hardness, being capable of scratching topaz, and 



