SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



Counterfeiting. — The blue stones which may be mistaken for, or passed off as, 

 sapphire are cordierite ("water-sapphire'"), kyanite (sappare), blue tourmaline ("indicolite"'), 

 blue topaz, and blue spinel. Amongst such stones may perhaps be included also haiiynite, 

 blue diamond, and aquamarine, which in some eases may resemble the sapphire. All, 

 however, without exception, differ from the sapphire in density, most of them being 

 considerably lighter and floating in the heaviest liquid, while corundum sinks heavily ; 

 spinel and kyanite alone have a density near that of this liquid (sp. gr. = 3'6). With the 

 exception of diamond these stones, too, are all considerably softer than corundum, by which 

 they can easily be scratched ; many of them, indeed, may be scratched even by topaz. 



Blue tourmaline, moreover, may be distinguished from sapphire by the difference in 

 the tone of its colour, which is an indigo-blue. Kyanite again is characterised by the 

 existence of a system of fine rectangular cracks, which are absent in the sapphire, and are 

 due to the presence of perfect cleavages and twinning. The blue of kyanite, however, is very 

 similar to that of sapphire, hence the name sappare, but its transparency is less perfect. 

 Cordierite is characterised by its very strong dichroism, far stronger than that of sapphire. 

 The specific gravity of topaz is its most salient distinguishing feature. Diamond, spinel, 

 and hauynite are singly refracting, and show no dichroism ; the same is true also for blue 

 glass, but this substance may be recognised also by its softness. 



The colour of sapphire is easily imitated in glass by adding to the strass a little cobalt 

 oxide, one part of cobalt oxide to seventy or eighty parts of strass giving a very fine 

 sapphire-blue colour. The same effect may be produced under certain conditions by the 

 use of iron. Thus, chemical analysis has shown that the beautiful blue colour of an antique 

 vase, ornamented with bas-relief in white, now preserved in the British Museum, is due not 

 to cobalt but to iron. The blue colour of the slag from iron furnaces is also due to the 

 same metal. It is not, however, customary at the present day to use iron for the purpose 

 of colouring glass. 



White sapphire, diamond, colourless spinel, zircon, topaz, rock-crystal, and phenakite, 

 as well as colourless strass, may each be mistaken the one for the other by the uninitiated. 

 Of these, sapphire, zircon, and spinel sink slowly in the heaviest liquid (sp. gr. = 3"6), 

 while all the rest float. Diamond only is capable of scratching leuco-sapphire, while 

 this itself scratches all the others. Glass, diamond, and spinel are singly refracting, and 

 can thus be distinguished from the other stones mentioned. Taking into account all these 

 differences, it should not be a matter of gi-eat difficulty to distinguish a colourless sapphire 

 from the colourless stones it somewhat resembles. 



OTHER COLOUB,-VAEIETIES OF PRECIOUS CORUNDUM. 



In addition to the true or oriental ruby and the oriental sapphire there are other 

 varieties of transparent corundum, which are distinguished from these and from each other 

 solely by their colours. We have already seen that these varieties are known by the name 

 of some precious stone which they resemble in colour with the qualifying prefix " oriental." 

 Thus certain of these colour- varieties of corundum are referi-ed to as " oriental aquamarine," 

 " oriental emerald," " oriental chrysolite," " oriental topaz," " oriental hyacinth," and 

 " oriental amethyst." The precious stones from which these varieties take their names are 

 sometimes given the prefix " occidental " ; all are softer than corundum and are easily 

 scratched by it. With the exception of zircon (hyacinth), the specific gravity of which is 

 greater than that of corundum, all the "occidental" are lighter than the "oriental" 



