QUARTZ (SMOKY-QUARTZ) 479 



14 by 14 by 9 inches. From one crystal a perfectly flawless sphere measuring 5^ inches in 

 diameter has been cut ; larger balls, with a diameter of 7i inches, are not entirely free from 

 flaws. The rock-crystal of this locality thus rivals in size and transparency that of Japan, 

 Brazil, Madagascar, and the Alps, which have hitherto been almost the only sources of such 

 material. 



Under some circumstances rock-crystal may be mistaken for other water-clear pi'ecious 

 stones, and being cheaper is sometimes successfully substituted for one or other of these 

 colourless gems. The resemblance to diamond in some of its features is indicated by the 

 number of names given in different parts of the world to this stone in which the word 

 diamond figures as an affix. Thus it is known as " false diamond" or "pseudo-diamond," 

 and, according to the locality in which the crystals occurs, as " Marmorosch diamonds," 

 " Schaumburg diamonds," " Arkansas diamonds," " Bohemian diamonds," " Irish diamonds," 

 " Paphos or Baffa diamonds," " Fleurus diamonds," " Bristol diamonds," " Isle of Wight 

 diamonds," " Quebec diamonds," and so on, and generally as " occidental diamonds." All 

 these terms signify one and the same stone, namely, rock-crystal, and since even the finest 

 specimens are not for a moment comparable either in brilliancy, lustre, or play of colours 

 with diamond, any real confusion seems impossible. 



In case of necessity rock-crystal and diamond can be distinguished by the help of the 

 facts that the former is doubly and the latter singly refracting, that the diamond quickly 

 sinks while rock-crystal floats in pure methylene-iodide, and also by the enormous difterence 

 in hardness between the two. The specific gravity of rock-crystal serves to distinguish it 

 from all other colourless stones. These, arranged in order of density conunencing with 

 the heaviest, are : zircon, sapphire, topaz, spinel, tourmaline, and phenakite. Phenaki te, 

 the lightest of these, has a specific gravity of 2-99, so that it is considerably heavier than 

 quartz, which has a density of £-65 and remains suspended in the lightest test liquid, in 

 which all the other stones sink. 



Although rock-crystal is so cheap and abundant glass imitations are often substituted 

 for it, and many of the so-called false diamonds are in reality nothing but glass. Genuine 

 rock-crystal is always considerably harder, and often also lighter, than the glass imitations ; 

 the two can be readily distinguished by the help of the polariscope, rock-crystal being 

 doubly, and glass singly refracting. 



SMOKY-QUABTZ. 



This is a transparent variety of quartz which is brown to almost black in colour. It is 

 often called " smoky topaz," but has no connection whatever with topaz. Smoky-quai'tz 

 when perfectly transparent is not infrequently cut, and with its deep, rich colour makes a 

 rather effective gem. 



The colour ranges from clove-brown to smoke-grey, passing by imperceptible stages to 

 the perfect colourness of rock-crystal, and, on the other hand, through darker and darker 

 shades till we reach specimens which, at any rate, in thick pieces, are almost perfectly black. 

 Such dark smoky-quartz is distinguished as morion. Specimens of this stone are not 

 always uniformly coloured, some portions being lighter and others darker. All darkly 

 coloured smoky-quartz is distinctly, though feebly, dichroic, the two dichroscope images 

 being coloured respectively yellowish-brown and clove-brown tinged with violet. The paler 

 the colour of the stone the less the difterence in colour between the two images, and the 

 dichroism of very pale stones is scarcely observable at all. A crystal of smoky-quartz is 



