QUARTZ (CHRYSOPRASE) 497 



is found principally in the KyfFhiiuser mountains, the petrified trees being enclosed in 

 sandstones and conglomerates of Permian (Rothliegende) age. Other localities for petrified 

 wood are extremely numerous, but need not be enumerated here; it may, however, be 

 mentioned that silicified wood, often in the form of gigantic trees, occurs in great abundance 

 in the Western States of North America, for example, in Colorado, California, and Arizona, 

 the petrified forest known as Chalcedony Park being situated in the last named State. The 

 material is often cut in these States, more frequently as an ornamental stone for table-tops, 

 pedestals, &c., than as a gem. 



Under the mineralogical term beekite are included silicified corals, the petrifying 

 material of which is quartz of much the same character as hornstone. Material in which 

 the white coral is thrown up against a fine flesh-red background is at present cut under the 

 name of " coral-agate " ; according to the Oberstein lapidaries the rough material is 

 obtained from the neighbourhood of Aden, Arabia, but similar material is also to be 

 obtained elsewhere. 



Chrysoprase. — Chrysoprase is a very fine-grained, moderately translucent hornstone 

 of a beautiful apple-green colour. It possesses all the usual characters of hornstone, 

 including the rough splintery fracture. The colour, which retains all its beauty in artificial 

 illumination, is never very deep, and the palest shades are almost colourless. 



The colour of chrysopi'ase, which can be seen on turning to the representation of a cut 

 stone in Fig. 8 of Plate XX., is due to the presence of about 1 per cent, of nickel. 

 This element is probably present in the form of a hydrated silicate, which, when heated, 

 loses water and becomes decolourised, since the stone itself, when exposed to the action of 

 heat becomes paler and paler, and finally quite white. The temperature necessary to 

 produce this change is not very high, and a seal of chrysoprase, if frequently used, will 

 gradually lose its colour. The same thing happens, moreover, \\hen the stone is exposed to 

 the direct rays of the sun, the decolourisation in the latter case being due not to the 

 action of heat but to that of light. 



That the decolourisation of chrysoprase is due to loss of water is demonstrated by the 

 fact that the colour is restored by burying the stone in moist earth or cotton-wool. The 

 colour of a bleached chrysoprase can be restored, or that of a pale stone improved, by 

 immersion in a solution of nickel sulphate. It is even possible to produce chrysoprase 

 artificially by immersing chalcedony for some time in a green solution of a nickel salt. 

 This is sucked up into the pores of the chalcedony, and imparts to it the fine apple-green 

 colour of true chrysoprase. It is sometimes almost impossible to distinguish these 

 artificially coloured stones from true chrysoprase, and a great many are sold as genuine 

 stones. The deception in such cases is not very serious, since artificially coloured chalcedony 

 agrees in almost all its characters with natural chrysoprase, and, indeed, possesses some 

 advantages over the latter, for its colour is usually finer and more uniform, and it is 

 unaffected by exposure to light and heat. 



Natural chrysoprase is rather diflScult to work, being very liable, on account of its 

 brittleness, to crack and splinter at the edges. Moreover, it must not be allowed to become 

 over- heated during grinding since this has a prejudicial effect on the colour. A stone 

 which has been over-heated not only loses its bright apple-green colour but also, to a great 

 extent, its translucency. If reasonable care be taken in the process of grinding, the colour 

 is retained unaltered, and after polishing the stone acquires a very fine lustre. Chrysoprase 

 is usually cut with a convex or plane surface, which is frequently bordered with one or two 

 series of facets (Plate XX., Fig. 8). It is suitable for ring-stones, pin-stones, &c., but not 

 for seals and signet-rings, because of its tendency to be decolourised by heat. It was at 



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