486 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



have recently been opened up again owing to the increased demand for amethyst : the best 

 material, of a rich purple colour, now obtained at this place fetches 120 to 800 francs per 

 kilogram, according to the size of the rough pieces. Nowhere, however, except in the 

 countries mentioned above, is amethyst mined to any appreciable extent. 



Amethyst is cut most frequently as a table-stone or in the step-cut (Plate XVIII., 

 Fig. 1 b), the brilliant form being rarely adopted. Stones of a deep, uniform colour are 

 mounted a Jour without foils, but pale or patchy stones are mounted with a foil of the same 

 colour. Fine large amethysts of a uniform colour now fetch from 10s. to 1 2s. per carat ; 

 they were formerly worth very much more, as can be gathered from the fact that at the 

 beginning of the nineteenth century the celebrated amethyst necklace of Queen Charlotte of 

 England was valued at d&SOOO, while at the present day it would scarcely find a purchaser 

 at d&lOO. The large amount of fine material, discovered during the course of the nineteenth 

 century in South America, is partly responsible for the depreciation in the value of 

 amethyst. Previous to this it was a costly material for superior jewellery, now it is used 

 principally for simpler and cheaper ornaments. Pale coloured or patchy stones are almost 

 valueless, the rough material fetching only a few shillings a pound. 



In ancient times amethyst was often used for seal-stones and engraved with various 

 devices, beside being fashioned into larger objects, such, for example, as the bust of Trajan, 

 carried off by Napoleon from Berlin. At the present day amethyst is but little used for 

 such purposes. 



On account of the similarity in colour between true amethyst and the far more valuable 

 " oriental amethyst," it is possible to mistake the one for the other, unless it be remembered 

 that the latter is far harder and heavier, and sinks in methylene iodide, while the former 

 floats. True amethyst is distinguished from violet fluor-spar, the so-called " false amethyst," 

 by its double refraction, greater hardness, and lower specific gravity. The double refraction 

 of true amethyst also distinguishes it from violet coloured glass, which from its appearance 

 alone is often not to be distinguished from the genuine stone. Artificially coloured violet 

 quartz is obtained by strongly heating rock-crystal and then immersing it in a solution of 

 some violet coloured substance. The colouring matter penetrates the cracks in the rock- 

 crystal caused by the sudden change of temperature, and, on drying, imparts its colour to 

 the stone. Stones which have been subjected to this treatment are easily recognisable on 

 account of the cracks, and for the same reason they are seldom cut. 



CITRINE. 



The name citrine is applied to yellow quartz. The crystals of this variety are 

 developed in the same way, exhibit the same two sets of striations meeting at an angle on 

 the pyramid face, and in many specimens the fractured surface has the same rippled, striated 

 character as in amethyst. It is obvious, therefore, that citrine differs from amethyst solely 

 in colour, and even this can scarcely be regarded as a fundamental difference, seeing that 

 amethyst assumes the colour of citrine when exposed to the action of heat. Some, indeed, 

 have gone so far as to assert that yellow quartz seldom or never occurs in nature, and that 

 the greater part of the yellow quartz now in existence is in reality " burnt " amethyst, or 

 possibly "burnt" smoky-quartz, the brown colour of which is, as we have seen, changed to 

 yellow under the action of heat. This assertion, however, is certainly incorrect, for citrine 

 does undoubtedly occur in nature at the localities to be presently mentioned, sometimes in 

 considerable amount. 



