102 



The formula given above requires 



Silica 28.56 



Alumina ^ 32.06 



Protoxide of iron 33.60 



Water 5.60 



100.02 



This, it will be seen, agrees very nearly with the results of 

 the analysis ; I would thei'^fore suggest that the name of Mason- 

 ite should be retained for the hydrous chloritoid, as the formula 

 given by Erdmann has been generally adopted for what is sup- 

 posed to be the real chloritoid. 



Mr. Whitney made some remarks on the remarkable vein of 

 black oxide of copper which was formerly worked at Copper 

 Harbor, Lake Superior, but which was abandoned after some 

 forty or fifty thousand pounds of this very valuable ore had been 

 raised. It was the only vein of this substance, and perhaps 

 the only locality known in the world, and specimens will be 

 highly prized by the mineralogist hereafter. The substance 

 called copper-black, and sometimes, black oxide of copper, which 

 occurs in an earthy, pulverulent form, is not to be confounded 

 with the pure oxide of copper found at Copper-Harbor. Copper- 

 black is a mixture of various hydrated oxides, especially of iron, 

 manganese, and copper, of which the latter forms but a small 

 portion ; it occurs as an incrustation on other ores of copper, 

 and is evidently the result of their decomposition. Semmola, 

 l;iowever, has described a substance occurring in small tabular 

 crystals, belonging to the hexagonal system, which, according to 

 him, are pure oxide of copper, Cu. To this substance he has 

 given the name of Tenorite. The oxide of copper found at 

 Copper-Harbor is generally compact, though the purer specimens 

 have a crystalline structure. Mr. Teschemacher has, however, 

 two specimens, which he has kindly allowed me to examine, in 

 which this substance is distinctly crystallized in cubes, with their 

 solid angles replaced. The question arises, was the substance 

 described by Semmola as crystallized in the hexagonal system, 

 really Cu, or is this substance dimorphous ? 



Some portions of the oxide of copper from Copper-Harbor 

 are almost chemically pure, though it is generally mixed with a 



