COLLECTIONS IN ECONOMIC GEOLOGY AND METALLURGY. 37 



All galenite coutains more or less silver, and fre^iueutly in our West- 

 ern States the silver is the most valuable constituent. The amount of 

 silver required to rouder a galena ore sufficiently argentiferous to be 

 called au ore of silver varies greatly, depending- on the circumstances 

 of its occurrence. It also frequently contains gold, sometimes visibly, 

 and generally contains, even in the purest specimens, small amounts of 

 other sulphides. To illustrate the occurrence of galena five specimens 

 are shown. 



(1) A single large aud distorted cube with small octahedral faces. Mine La Motte, 

 Madison County, Missouri. (17137.) 



('2) Crystallized, an aggregate of cubes with octahedral faces. Joplin Mine, .Jopliu, 

 Jasper County, Missouri. (17590.) 



(3) Crystallized, separate cubes with octahedral faces on dolomite. Seed Lick 

 Diggings, Mine La Motte, Madison County, Missouri. (17126.) 



(4) Crystallized, single cubes with small octahedral faces. All the faces have a thin 

 coating of pyrite. Joplin, Jasper County, Missouri. (17.592.) 



(5) Massive, showing the cubic cleavage in perfection. Missouri. (65208. ) 



Many massive specimens of galena may be seen in the silver-lead ore 

 series. 



ANCtLESITE. 



Composition: PbS04. Sulj)hate of lead, containing oxide of lead 

 73.6 per cent, (lead 08.4 per cent.), and sulphuric acid, 2G.4 per cent. 



It crystallizes in the orthorhombio system, crystals being complex, and 

 frecpiently tabular or octahedral in habit, occasionally occurs stalactitic 

 and sometimes massive. It varies in hardness from 2.75 to 3, and in 

 specific gravity from G.12 to 6.31). It has an adamantine luster and is 

 colorless or slightly tinged and transparent. 



Anglesite is generally associated with, and is theresultof, the decom- 

 position of galena, when, however, it has been subjected to the action 

 of carbonated waters it is readily changed to the carbonate of lead, 

 cerussite. It is always more abundant in the upper levels of a mine. 

 To illustrate the occurrence of anglesite three specimens are shown. 



(1) Transparent white crystals, on galena. Elkhead, Christian County, Missouri. 

 (64283.) 



(2) Transparent white crystals, in a cavity in galena. Modoc Mine, Leadville, 

 Lake County, Colorado. (56446.) 



(3) Massive, showing the cubic outlines of the original galena. Madonna Mine, 

 Monarch, Chaffee County, Colorado. (51539.) 



In the collection from the Colorado smelter may be seen several 

 specimens of anglesite associated with both unaltered galena and cerus- 

 site. 



CERUSSITE. (WHITE LEAD ORE.) 



Composition : PbCOs. Carbonate of lead, containing oxide of lead 

 83.5 per cent, (lead 77.5 per cent.), and carbonic acid 16.5 per cent. 



It crystallizes in tli(^ orthorhombic system, crystals usually thin, tab- 

 ular, aud very frequently twinned, often found granular, and sometimes 



