212 SILVER DEPOSITS AT BUTTE, MONTANA TERRITORY 



The silver and lead sulphides which, are found below the zone of 

 oxidising influences, are changed into chloride in the case of 

 silver, and the lead into carbonate ; and in one case I have recog- 

 nised the rare mineral minium (Eed oxide of lead). 



In almost every case the granite, in contact with this oxidised 

 vein matter, has been partially decomposed, the felspar has been 

 converted into kaolin, and the whole rock has been stained and 

 blackened by the oxides of manganese and iron. It frequently 

 contains, however, sufficient silver (as chloride of silver), to yield 

 a profit in working. 



NOTE ON THE ARTIFICIAL FORMATION OF DIOXIDE OF COPPER, 



" CUPRITE." 



By R. PEARCB, June., P.G.S. 



This compound (a specimen of which I send) was found attached 

 to the sides of a wooden tank, in which dilute sulphate of 

 copper solution had been kept — undistiu'bed, and at an even 

 temperature of about 180° Fah. for one year. When viewed 

 under the microscope by transmitted light, the crystals shew the 

 beautiful ruby-red colour, so characteristic of the natural mineral, 

 and the same modifications of crystals may also be seen. Cube, 

 with faces of the octahedron, and rhombic dodecahedron. 



I cannot account for their formation, unless we suppose that 

 the reducing action of the juices of the wood effected this change 

 on sulphate of copper. It is not improbable that a similar change 

 takes place in copper lodes, where cuprite is commonly found in 

 gossans near the surface, the action of the water, containing 

 humous matter in solution, might have the effect of reducing 

 solutions of sulphate of copper into dioxide of copper. 



