THE ORES. 53 



Anglesite (sulphate of lead) is an important mineral in the compo- 

 sition of the Eureka ores. It forms a large portion of the "yellow car- 

 bonate" of the miner, and is present to some extent in all the lead-bear- 

 ing ores of the hill. It is the product of the decomposition of the galena, 

 and occurs in three forms: as colorless crystals in geodes in the galena and 

 other ores in a manner that shows that it was deposited from a solution of 

 the sulphate; in compact masses of a dull black color, usually containing 

 undecomposed sulphide and a kernel of galena; and in finely divided par- 

 ticles disseminated throughout the ore. In the latter case it is not distin- 

 guishable by the eye, and its presence can only be detected by the usual 

 tests for sulphuric acid and lead. 



Cerussite (carbonate of lead) almost always occurs crystallized, some- 

 times in acicular crystals mixed with other minerals throughout the ore ; 

 sometimes in geodes and surrounding nodules of galena and anglesite, 

 and in massive aggregations of small crystals of a dark color. In this lat- 

 ter instance it is called "sulphuret ore" by the miners, and probably con- 

 tains an admixture of mimetite, as arsenic acid can often be detected by 

 means of the blow-pipe. The dark color is due to the presence of manga- 

 nese. It is evidently the ultimate product resulting from the decomposition 

 of the galena after that mineral had been changed into sulphate. It seems 

 also to exist disseminated in a finely divided state throughout the so-called 

 "red carbonate," a mixture of different lead minerals and hydrated oxide of 

 iron, for this ore gives a reaction for carbonic acid while it contains scarcely 

 any lime. 



Mimetite (chloro-arsenate of lead) is found in colorless crystals 



"Analysis of colorless inimetite from the Richmond mine, Eureka, Nevada, by F. A. llassie, of 

 the University of Virginia : 



The specimen consisted of slender, almost acicular, hexagonal prisms, aggregated into a friable 

 mass, with a few small crystals of wulfenite scattered throughout it. The individual crystals were color- 

 less and transparent, with adamantine luster and white streak, the general aspect of the mass very 

 much like that of cerussite. Hardness = about 3; sp. gr. = 6.92; very easily fusible. Analysis gave: 



As.,0 5 23.41 



Pbj0 6 trace 



PbO 68.21 



PbCl 2 8.69 



100.31 

 In accordance with the well-known formula : 



PbCl 2 . SPbaAsjOs. 



