120 Examination of a few American Minerals. 



Island. We have four (or six including those under water) 

 beds of limestone, with their associated shales and limestone 

 shales, the former metamorphosed into marble, and the latter 

 into gneiss and calciferous gneiss — granite or hornblende. 



The conclusion which we have arrived at is, that the rocks 

 of New York Island are metamorphosed Taconic, and worthy 

 of the name of Manhattan Group. 



XI. — Examination of a few American Minerals. 



By Charles A. Joy, 

 Professor of Chemistry, Columbia College, New York. 



Eead May 15, 1865. 



1. Silicate of Copjyer, Chrysocolla, Copper Harbor, Lake 



Superior. 



This specimen was one of the earliest brought from Lake 

 Superior, and was interesting on account of the proximity of 

 the locality to the remarkable deposit of black oxide of copper 

 found near Copper Harbor. 



It was supposed by early explorers to be a carbonate, and 

 the " pocket" of black oxide was looked upon as having been 

 derived from the chemical decomposition of this mineral, 

 known as " the green rock." 



For the determination of the water, 1*294 grms. of the finely 

 pulverized mineral, dried at 100° C, were heated to redness 

 until the weight remained constant. Loss of weight, 0-3429 

 grms. = 26*50 per cent. The powder was decomposed by 

 nitric acid ; found silica, 0414 grms. = 32 per cent. The iron 

 and alumina were precipitated, by ammonia, found 0*1002 grms. 

 = 7*75 per cent. The copper was precipitated by caustic pot- 

 assa, and determined as oxide ; found 0-423 grms. = 32.75 per 

 cent. 



