TRANSPARENT STONES 



575 



often by the possession of a milky sheen. " Oriental chrysolite " is also capable of 

 scratching topaz, but is much more strongly dichroic than is chrysoberyl. Zircon of this 

 colour is rare ; it has a strong adamantine lustre, and is far denser than any other stone 

 in the division, so that an exact determination of the specific gravity of this stone is sufficient 

 to establish its identity. Demantoid is the only singly refracting stone included in this 

 division. 



In Division II. topaz is characterised by its hardness, and is the only stone in this 

 division which is capable of scratching quartz. The characters of many of these mh._..*l 

 have been considered already ; chrysolite is harder than sphene, and much less dichroic than 

 epidote or idocrase. Not infrequently the specific gravity of chrysolite is exactly the same 

 as that of methylene iodide, the stone will therefore sink slowly as the liquid is warmed 

 or rise to the surface as it is cooled, the contact of the vessel with the warm hand being 

 sufficient to cause the stone to rise. " Oriental chrysolite " is much heavier, much harder, 

 and much more strongly dichroic than is true chrysolite. 



Division III. includes hiddenite, andalusite, and tourmaline ; all three are dichroic, but 

 andalusite is most strongly so, and is characterised further by one of the dichroscope images 

 being red. Andalusite and tourmaline scratch quartz, but hiddenite does not. 



The variety of beryl known as " aquamarine-chrysolite " is recognised by its low specific 

 gravity and feeble dichroism. 



Moldavite is singly refracting, and is distinguished from artificial yellowish-green glasses 

 only by its lower specific gravity. 



14. GBEEN STONES. 



In the first division the green variety of corundum, known as " oriental emerald," is 

 iery rare. Zircon and demantoid are uncommon, and dark green chrysoberyl (alexandrite) 



