136 ECONOMIC GEOLOGY 



fore occurs both as native copper and in its numerous compounds. 

 Copper is found in small quantities in the igneous rocks and there- 

 fore in the sedimentaries derived from them. It is a common 

 constituent of sea water, and the green color of the sea has been 

 attributed to its presence. Copper has been obtained in the 

 ashes of sea weeds and found in certain varieties of corals. 



According to F. W. Clarke, native copper is commonly, if not 

 always, of secondary origin, either deposited from solution or 

 formed by the reduction of some solid compound. Pseudo- 

 morphs of copper after cuprite are well known. W. S. Yeats has 

 described pseudomorphs of copper after azurite from Grant 

 County, New Mexico. W. Lindgren states that the vein of 

 metallic copper at Clifton, Arizona, appear to have been derived 

 from Chalcocite. T. Carnely has shown that native copper is 

 soluble in saline water. Small quantities of native copper have 

 been found at both the Ely mine in Vershire, Vermont, and in the 

 Corinth mine in Cornith, Vermont, that appear to have been 

 formed from very dilute sulphate solutions. The greatest known 

 deposits of metallic copper are found in the Lake Superior region. 

 F. W. Clarke states its original home was, perhaps as sulphide, 

 in the unaltered igneous rocks, but its concentrates are now found 

 in the sandstones, conglomerates, and amygdaloids. In the 

 sandstones and conglomerates it acts as a cement. It also re- 

 places pebbles and even boulders a foot or more in diameter. A. 

 C. Lane has cited a corroded quartz crystal which was mainly 

 replaced by copper. Frequently native copper has been reported 

 as holding enclosed nodules of native silver. According to F. W. 

 Clarke, if these metals had been deposited from a fused magma 

 they should not have solidified separately, but as an alloy. 



R. Beck mentions native copper filling the marrow cavities of 

 fossil bones in the Peruvian sandstones of Corocoro, Bolivia. 

 E. Haworth cites films of copper in the shales near Enid, 

 Oklahoma, which were precipitated by organic substances. 



The largest single mass of native copper ever found was dis- 

 covered in the Minnesota mine, Michigan, in February, 1857. 

 It was 45 ft. long, 22 ft. wide and 8 ft. thick. It weighed 420 

 tons. It was 90 per cent, pure copper and contained an appre- 

 ciable amount of silver. The value of that single specimen at 

 the average price of copper would be about $83,000. 



Chalcopyrite is the most important ore of copper. Bornite 

 and chalcocite are next in importance at least among the sulphides. 



