506 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



COMMON CHALCEDONY. 



This is chalcedony in the more restricted sense, and is known simply as chalcedony. 

 In colour it is white or some very pale shade of grey, yellow, brown, blue, or green ; though, 

 as a rule, it is uniformly coloured, specimens are sometimes met with which show cloudy 

 patches (cloud-chalcedony) and an indistinct banding. Common chalcedony is built up of 

 layers just as agate is, but being all of the same colour the banded structure is inconspicuous ; 

 specimens in which it is at all prominent are referred not to common chalcedony but to 

 agate. As examples of chalcedony with a pronounced colour may be mentioned the rare 

 sappJiirine of lapidaries found at Nerchinsk in Siberia, in Transylvania, and in India, which 

 approaches in colour the blue of the sapphire, and the yellow ceragate (wax-agate or semi- 

 carnelian), which has a waxy lustre. Cloudy milk-white chalcedony is referred to as white 

 carnelian. 



The fibrous structure of common chalcedony is fairly apparent : the fracture is typically 

 uneven and finely splintery, and the lustre of the fractured and of a cut and polished surface 

 agrees with the description already given. Though never perfectly clear the mineral is 

 often very translucent, even in thick pieces, but in other cases, especially in milk-white 

 stones, it is almost opaque. Very translucent stones are termed " oriental chalcedony " to 

 distinguish them from more opaque specimens, which are described as "occidental chalce- 

 dony." The finest " oriental " specimens are not always perfectly translucent throughout, 

 but show delicate cloudy patches, which are by no means prejudicial to their beauty, but 

 rather the reverse. 



Common chalcedony occurs as reniform, botryoidal, and stalactitic incrustations on the 

 surface of rocks, and also as a filling in of the cracks and crevices of these same rocks. It 

 is of moderately wide distribution, but usually occurs only in small amount, the incrustations 

 being too thin to admit of the material being cut. Thicker masses of greater purity and 

 beauty come from Iceland and the Faroe Islands, and a considerable amount also from 

 India. The Indian localities will be enumerated below under agate. 



Chalcedony was more extensively used both formerly and in ancient times than now, 

 its place having been taken by other stones. It is cut for ring-stones and seal-stones, and 

 it also furnishes a material for seal-stocks, cups, plates, bowls, vases, &c. It is worked in 

 Europe, principally at Oberstein and Idar on the Nahe, and at Waldkirch in Baden. A 

 considerable amount is done also in India, but the industry is of less importance there than 

 in Germany. 



It is only exceptionally large and fine specimens of chalcedony which have any 

 considerable value. The value of a stone depends principally on its translucency and on 

 the uniformity of its colouring; it is important also that there should be no cracks or faults 

 of other kinds. Cloudy, patchy, or fractured stones are practically worthless. In spite of 

 the fact that chalcedony is so abundant and so low in price, it has been closely imitated in 

 glass ; such imitations, however, can be distinguished from the genuine stone by the fact 

 that they are less hard, and that their specific gi-avity is higher. A few varieties of common 

 chalcedony are sometimes distinguished by special names, for example : 



Spotted agate (spotted chalcedony, St. Stephen's stone) is a white or greyish 

 chalcedony with small red spots. In the finest specimens the spots are no bigger than dots, 

 and these are distributed uniformly over the whole surface so closely that when viewed at 

 some distance the stone appears to be of a uniform rose-red colour. 



Mocha-stone (tree-stone or dendritic agate) is a white or grey chalcedmiy showing 



