572 



DETERMINATION OF PRECIOUS STONES 



Zircon, hessonite, topaz, and citrine can be readily distinguished by the help of the character 

 tabulated above and by the remarks appended to previous tables. 



Amber diffei's from all the other members of this group in feeling warm to the touch, 

 and in the fact that it acquires a strong charge of electricity on being rubbed. 



Glass and opal are distinguished in the way indicated under the preceding table. 



9. SMOKE-GREY AND CLOVE-BROWN STONES. 



Of the stones of this group, practically the only one which is widely distributed is 

 smoky-quartz. Andalusite and epidote are rare, and axinite still more so, but brown 

 diamond is less uncommon. The characters given in the table are sufficient to distinguish 

 any one of these stones from any other, and from glass without much difficulty. 



It is sometimes a little difficult, however, to discriminate between epidote and idocrase, 

 and one has to rely on the fact that the former is more strongly dichroic than the latter. 



Andalusite is distinguishable from axinite by the greenish tint of its colour, and by the 

 fact that the dichroscope images are differently coloured. 



10. REDDISH- YELLOW STONES. 



The characters which distinguish pyrope, hessonite, and spinel one from another have 

 been given already under Table 7. Hessonite and hyacinth are sometimes very similar in 

 colour, and are often mistaken the one for the other, in spite of the fact that hyacinth has a 

 much stronger adamantine lustre than has hessonite ; there is also a fundamental difference 

 between them in the character of their refraction, hessonite being singly and hyacinth doubly 

 i-efracting. " Oriental hyacinth " is distinctly dichroic, but the hyacinth variety of zircon is 

 only vei"y feebly so. 



