412 Washington — Copper Crystals in Aventurine Glass. 



the last century, and was only re-discovered after the recent 

 revival of the art some thirty years ago, due chiefly to the late 

 Dr. A. Salviati of Yenice. The glass finds now quite an 

 extensive use in the manufacture of mosaics and of brooches 

 and other cheap jewelry. 



According to Yogt* it was one of the first substances of a 

 mineralogical nature ever examined with the microscope, since 

 in 1807 I. G. Gahn in Fahlun called Hausmann's attention to 

 the fact that small three- or six-sided tables were visible in it 

 under the microscope. Wohlerf was the first to show that 

 these tabular crystals were of metallic copper, to whose brilliant 

 reflections and metallic luster the peculiar appearance of the 

 glass is due. Although, to judge from a remark of Yogt's 

 (see below), the glass has been several times examined, yet I 

 can find but two references to it in the literature at my dis- 

 posal here. Fouque and Levy:]; simply mention Wohler's 

 determination of the character of the crystals, while J. H. L. 

 Yogt§ devotes a couple of pages to it, and gives a few figures, 

 but goes little into details. 



Through the kindness of Signor G. Boni of Rome, to whom 

 I desire to express my thanks, I was enabled to obtain at the 

 works of the Yenezia-Murano Glass Co. at Murano specimens 

 not only of the finished perfect product, but of a mass that 

 was the result of an unsuccessful melting, as well as fragments 

 of the melting pots both before and after their exposure to 

 the intense heat of the furnaces. The results of a microscop- 

 ical examination of this material seemed worthy of publica- 

 tion, especially since they add to our knowledge of the crys- 

 tallization of copper. 



The perfect glass is of a copper brown color, and transparent 

 to translucent in thin flakes, showing on the edges a pale 

 brown color. It is filled with innumerable small flakes and 

 spangles of a slightly brownish yellow color and brilliant 

 metallic luster. This is best seen apparently in sections or 

 fracture surfaces of the glass parallel to the original surface in 

 the melting pot, showing that the majority of the flakes lay 

 horizontally in the molten glass. The specimens also show 

 streaks of comparatively flakeless material. 



The imperfect glass is slightly darker in color and is less 

 transparent, showing at the thin edges a greenish color. The 

 spangles and glistening points are almost entirely wanting and 

 those present much smaller than in the perfect examples. A 

 specimen taken from the surface of the mass solidified in the 



*Vogt, Mineralbildung in Schmelzmassen. Kristiania, 1892, p. 238. 

 ■f Wohler, Gott. gelehrt. Auz., v, 1842, p. 1785. 

 % Fouque et Levy, Synth, d. Min. et d. Roches. Paris, 1882, p. 367. 

 § Op. cit., pp. 237-9. 



