502 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



and in others the opaque jasper, the former being sometimes distinguished on this 

 account as agate-jasper and the latter as j asp-agate ; they are scarcely ever used as gems, 

 and none are of any importance. 



AVANTUEJNE. 



Avanturine or avanturine-quartz is a feebly translucent, fine-grained to compact 

 quartz, with a conchoidal or usually splintery fracture; the surface of which has a 

 speckled, metallic sheen, usually of a reddish-brown colour, but occasionally yellow, 

 white, blue, or green. This appearance is caused by the presence, in the colourless 

 quartz substance, of numbers of enclosures, which can always be seen with the aid of 

 the microscope, and sometimes with a simple lens, or with the naked eye. In some 

 cases these enclosures consist of small silvery, reddish-brown, or sometimes white, scales 

 of mica; in others of minute plates of the green chrome-mica fuchsite, or of similar 

 plates of a blue colour of some unknown mineral, while in other stones the sheen is 

 caused by the existence of numbers of small cracks filled with hydrated oxide of iron. 

 Each crack filled with this substance and every single scale of mica gives its own 

 metallic reflection; the sheen of the mass is the sum total of these reflections, and- 

 is the more uninterrupted the more uniformly and closely set in the quartz are these 

 enclosures. As a rule, reddish-brown avanturine closely resembles sun-stone, which for 

 this reason is called avanturine-felspar, avanturine itself being often called avanturine- 

 (juartz. The two can be distinguished by the fact that the quartz is the harder and 

 will scratch the felspar. 



Avanturine is often set in rings, pins, brooches, cuff-links, &c. It is cut with a 

 flat or slightly convex surface without facets, and acquires by polishing a fine, strong 

 lustre. The more uniform and uninterrupted is the sheen of a specimen of avanturine 

 the more valuable it becomes, and portions with a sheen of this discription are cut 

 out of the large irregular masses of poorer quality which occur in nature. Avanturine 

 was at one time much prized as a gem ; now, however, it is more frequently used as 

 a material for bowls, vases, and ornamental objects of various kinds, the sheen ' being 

 of course less perfect and uniform over objects of this size than over the surface of a 

 small gem. Reddish-brown avanturine with a coppery reflection is the most highly 

 esteemed variety ; other avanturine, such as the brown, reddish-yellow, white with a 

 silvery white sheen, black with white spots, green and blue, though rarer, are less prized. 

 The special beauty of avanturines is associated with the isolation of the glancing metallic 

 scales, and the consequent appearance of so many starry, glittering points. 



Avanturine is rather widely distributed, and specimens of considerable size are not 

 by any means rare, although those possessing the most desirable characters and of a 

 quality suitable for gems are not to be found at every locality. 



The mineral occurs both in primary deposits and also as loose pebbles. The richest 

 localities are in the Urals, where it is found, forming thick beds in mica-schist, at several 

 places in the Taganai range, to the north of Zlatoust on the Ui, a tributary of the Ufa. 

 Also at Kossulina, twenty-eight versts west-south-west of Ekaterinburg, the material found 

 here being superior in colour and sheen, but traversed by cracks and therefore not to be obtained 

 in large pieces. All the material found in this region is cut at Ekaterinburg. White and 

 reddish-white avanturine is found in the Altai mountains at Beloretzkaya, thirty versts from 

 the long-famous lapidary works at Kolivan (latitude about 51° N.) It is worked at Kolivan ; 

 and, together with the Uralian avanturine, has furnished material for the bowls, vases, and 



