ARTIFICIAL PRODUCTION 93 



5. Feathers. — Under this name are included cracks and fissures which may be present 

 in all kinds of precious stones, and which exert a disturbing action on the path of the rays 

 of light passing through the stone. They may be of large or of almost microscopic size, 

 and may occur singly or aggi-egated together in large numbers. They are especially common 

 in stones which possess a very perfect cleavage, such as diamond and topaz ; they then have 

 the direction, regularity and flatness peculiar to cleavage cracks. Faults of this nature are, 

 however, also present in stones which possess no marked cleavage, such as quartz and garnet, 

 but here they are irregularly curved and bent. In such cracks, brilliant, iridescent colours 

 are often to be seen, and when this is the case the cracks are more noticeable. The 

 existence of feathers, which do not exhibit such interference colours, is very difficult to 

 detect, even with a lens ; they may be best demonstrated by placing the stone in methylene 

 iodide. 



Feathers are more to be feared than any other kind of fault, since there is always a 

 tendency for these small cracks to extend, thus adding to the disfigurement of the stone, 

 and perhaps in the end causing its complete fracture. This is especially likely to happen 

 during the grinding, owing to the vibration consequent on the operation, or it may be 

 brought about by subsequent careless handling, and often even with no apparent cause. It 

 is therefore very desirable before going to the labour and expense of cutting a stone, to make 

 certain that it is free from such faults. This may be done as mentioned above, by 

 immersing the stone in a strongly refracting liquid and inspecting it with a lens. Another 

 method is to heat the stone and then quickly cool it by immersing it in cold water ; any 

 incipient cracks will be made to develop by this treatment and thus become more distinctly 

 visible, or the stone may even fracture along the cracks ; this operation is of course risky 

 and should not be attempted with valuable stones. 



6. Icy flakes. — These are small cracks which are not of natural occurrence in 

 precious stones, but are developed during the process of grinding if a stone has been allowed 

 to become too hot. Their presence is manifested as dull cloudy areas on the surface of the 

 stone which are incapable of receiving a good polish. Such faults can be avoided by keeping 

 the temperature of the stone down during the process of grinding. 



I. ABTIPICIAL PRODUCTION. 



As in the case of many minerals, it has been possible to produce the majority of 

 precious stones by artificial means. These artificial products are in every respect identical 

 with naturally occurring precious stones — namely, in their chemical composition, crystalline 

 form, and in all their physical characters. When it is possible to obtain such artificially 

 formed precious stones of sufficient size and of the clearness, transparency, and fine colour 

 of the naturally occuring precious stones, they will be equal in value to the latter, and 

 equally applicable to decorative purposes. To consider artificially formed stones inferior 

 to natural stones is nothing but baseless prejudice. They differ from the latter in no 

 respect save origin, having been produced under artificial instead of natural conditions ; 

 they are therefore truly genuine stones, and in no sense must they be regarded as 

 imitations. 



Many have been the experiments made with the object of producing minerals by 

 artificial means, and in numerous instances such efforts have been successful. In the 

 case of precious stones the results, although of the greatest scientific interest, have had, 

 up to the present, little or no practical importance, since the stones obtained have been but 

 of very small size, often microscopically minute, and thus useless as gems. Only in the 

 case of two of the more valuable precious stones, the ruby and turquoise, have results 



