130 SYSTEMATIC DESCRIPTION OF rilECIOUS STONES 



•eruption of Vesuvius. He proceeded to say further that the fragmentation of a diamond 

 may be effected by subjecting it to a preliminary immersion in the warm blood of a goat, 

 but that even under these circumstances the hammer and anvil will also be broken ! 

 According to Albertus Magnus (1205-1280), the blood is more eificacious if the goat has 

 previously drunk wine or eaten parsley ! 



Such being the views then held respecting the unbreakable and indestructible character 

 of the diamond, it is easy to understand why the Greek word adamas, signifying unconquer- 

 able, should have been applied to this stone, although its application to the diamond is 

 singularly inappropriate and inaccurate when its extreme frangibility is considered. Many 

 a doubtful stone has been submitted to the test of the hammer, with the belief that the 

 blow would be resisted only if the stone were a genuine diamond. Probably many beautiful 

 stones have been sacrificed to this old belief. As a matter of fact, diamond is easilv 

 fractured, a very moderate bloiv from a hammer sufficing for the purpose ; its perfect 

 cleavage places it among the most brittle of minerals. 



6. OPTICAL CHARACTERS OP DIAMOND. 



Transparency. — In its pure condition diamond is most beautifully clear and 

 transparent ; the presence of enclosures of foreign matter, however, often diminishes the 

 natural transparency of the stone, in some cases causing almost complete opacity. Dark 

 coloured diamonds, especially brown and black specimens, are frequently transparent only at 

 their edges, and black diamonds are often completely opaque. The transparency of a crystal 

 depends also upon the condition of its surface ; if this should be roughened, as will be the 

 case after a prolonged rolling about on the bed of a river, the stone will appear dull and 

 cloudy, although its interior may be perfectly transparent, as is evident when the rough 

 surfaces have been removed by cutting. 



On the degree of transparency depends largely the quality known as the water of a 

 diamond. A stone which is perfectly transparent, colourless, and free from all faults is 

 described as a diamond of the first or purest water. A small degree of cloudiness in a 

 diamond does not entirely unfit it for use as a gem ; when, however, the cloudiness exceeds 

 a certain amount the stone can be applied only to technical purposes. 



liUStre. — The lustre on the smooth face of a diamond, beside being extraordinarily 

 strong and brilliant, is very peculiar in character and is intermediate between the lustre of 

 glass and that of metal. Being characteristic of diamond, it is known as adamantine lustre, 

 and is shown by very few minerals and by still fewer precious stones. It is therefore 

 possible after a little practice to readily distinguish diamond from other transparent 

 substances, such as glass, rock-crystal, &c., by the character of the lustre alone. As we 

 have already seen, however, there is an artificial glass known as strass, which possesses an 

 adamantine lustre and which is therefore much used in the manufacture of imitation 

 diamonds. 



Adamantine lustre is frequently absent from the natural faces of diamond crystals 

 especially after they have become dulled by friction in a river-bed. In such cases, the stone 

 has a peculiar lead-grey metallic appearance, similar to that which is artificially produced 

 by bruting, an operation in the process of diamond cutting which consists of the rubbing 

 together of two diamonds with the object of obtaining an approximation to the form they 

 are finally to assume. Adamantine lustre is seen to perfection on the polished facets of a 

 cut diamond, since here the incident light is reflected quite regularly. The lustre of 

 diamonds which are dark coloured, and therefore have little transparency, approaches that 



