QUARTZ (AVANTURINE) 503 



ornaments ^vhich have been from time to time presented by the Czar of Russia to European 

 princes. A vase of this description was presented in 1843 by the Czar to Sir Roderick 

 I. Murchison in recognition of his services in exploring the geology of part of the Russian 

 Empire ; it is 4 feet high and measures 6 feet in circumference at its largest part ; it is 

 preserved in the Museum of Practical Geology, London. Large blocks of avanturine 

 of faultless quality are worth hundreds of pounds. 



Fine specimens of this mineral are occasionally met with in India, but nothing definite 

 is known as to their mode of occurrence or the exact locality. A very pretty green glisten- 

 ing variety from the Bellary district in Madras deserves mention ; the scales of mica enclosed 

 in it are of the green chromiferous variety known as fuchsite, and the mineral itself occurs 

 in blocks from which slabs of considerable size can be cut. 



Green avanturine of this description is very highly esteemed in China ; it is one of the 

 stones referred to as " yu " and is distinguished from the others as the imperial yu-stone. 

 The imperial seal is said to be made of this material, which is esteemed far more highly than 

 is nephrite. The locality from whence the Chinese obtain the stone is not known. 



Avanturine is said to have been found at several localities in Europe ; for example, in 

 the neighbourhood of Aschaifenburg in Bavaria, at Mariazell in Styria, and at Veillane 

 between Susa and Turin in Piedmont, where it is found as pebbles. Also at Nantes in France, 

 Glen Fernate in Scotland, and in the neighbourhood of Madrid, where it is associated with 

 pebbles of granite. 



Avanturine -glass is an artificial product which resembles natural avanturine but 

 possesses an even finer appearance. It is a colourless glass in which are embedded numerous 

 small red octahedra, the faces of which are equilateral triangles. The chemical composition 

 of the material, the well-defined crystalline form, together with the red colour and strong 

 metallic lustre of the enclosures, points to the fact that the latter consist of metalHc copper. 

 The much lower hardness of avanturine-glass, together with the form of the enclosures, 

 which can be readily made out with a lens, definitely distinguishes it in all cases from natural 

 avanturine (avanturine-quartz) and from sun-stone (avanturine-felspar). 



There is a rather improbable story to the effect that a glass-maker of Murano, near 

 Venice, discovered the art of making this glass by accident {par aventure), by dropping some 

 copper filings into molten glass, and that the name avanturine (or aventurine) originated 

 thus, and was afterwards applied to the natural mineral. It is very likely that the fable 

 was invented in order to preserve the secret of the art of manufacturing this magnificent 

 glass by putting curious inquirers off the scent. The art came subsequently to be forgotten 

 or lost, even in Murano, until the year 1827, when it was rediscovered by the glass-maker, 

 Bibaglia, after many unsuccessful trials. The chief difficulty is to prevent the copper from 

 separating out into clusters of crystals, and to obtain these crystals distributed regularly 

 throughout the whole mass of glass as is necessary in order to obtain the most favom-able 

 appearance. The product of this art, which is still a trade secret, is a most beautiful glass, 

 much finer than natural avanturine, and is much used in the manufacture of small ornamental 

 objects. It is possible to obtain large blocks of the material so that it can be used for 

 objects of considerable size. Avanturine-glass fetches from 40s. to 50s. per kilogram; 

 it contains about 2| per cent, of copper and is made of a very easily fusible glass, which 

 melbs at a much lower temperature than does the copper. 



