362 Mr. F. Field on the Silicates of Copper from Chile. 



translucent glass. Some short account of those minerals which 

 are found most frequently may perhaps not be entirely devoid of 

 interest. 



Green and Blue Silicates. — The Chilian miners frequently 

 meet with veins of hard blue or green mineral, which they term 

 Llanca, consisting, with the exception of small quantities of lime, 

 alumina, and oxide of iron, entirely of oxide of copper, silicic 

 acid, and water. The following is the composition of one of 

 these llancas, which was found coating thin veins of suboxide of 

 copper and the native metal, in the mines of Andacollo, Chile ; 

 the analysis was made by M. Domeyko : — 



Oxide of copper . . . 2950 



Silica 52-20 



Water 1670 



Alumina 1-20 



99-60 

 Another specimen of a pure green colour, analysed by the 

 same chemist, yielded — 



Oxide of copper . . . 12-00 



Silica 75-90 



Water 10-10 



Alumina 2-00 



100-00 

 Showing a very great difference in composition. 



I obtained from a mine in the neighbourhood of Tambillos 

 near Coquimbo, a considerable quantity of very fine silicate of 

 copper, having a pure turquoise-blue colour, with little or no 

 shade of green, perfectly amorphous and opake, and which 

 appears, as the analysis will show, to have a far more definite 

 composition than cither of the samples quoted above : — 

 Oxide of copper . . . 39-50 



Silica 28-21 



Water 24-52 



Oxide of iron .... 2-80 

 Alumina ..... 4-97 



10000 



Regarding the alumina and oxide of iron as foreign to the 

 mineral, we have in every 100 parts, — 



Oxide of copper . . . 42-83 



Silica 30-59 



Water 26-58 



100-00 

 Silicate of copper, consisting of one equivalent of silicic acid, 



