502 



KNOPF: PLUMBOJAROSITE FROM NEVADA 



An analysis of this mineral was made by Dr. R. C. Wells in 

 the laboratory of the U, S. Geological Survey. 



Analysis of basic lead-ferric sulphate, Yellotv Pine district, Nevada 



Si02.. 

 FejOa. 

 AI2O3. 

 H2O- 

 H2O+ 

 SO3... 

 PbO.. 

 NaaO. 

 K2O.. 

 CaO.. 

 MgO.. 



1.14 



38.90 



3.33 



0.94 



10.77 



24.60 



18.44 



0.76 



0.10 



0.45 



0.49 



99.92 



MOL. R.iTIOS 



0.243\ 

 0.033/ 



0.598 



0.308 



0.083^ 



0.012 



0.001. 



0.008 



0.012 



0.276 or 2.88 



0.598 or 6.23 

 0.308 or 3.21 



0.096 or 1 



Specific gravity: 3.458. 



The interpretation of this analysis presents some difficulty. 

 If the small amounts of silica, hme, and magnesia are neglected 

 as belonging to impurities, the ratios suggest the formula 

 PbO3Fe2O3.3SO3.6H2O, in which the lead has been isomorphously 

 replaced to a minor extent by sodium and potassium, and the 

 ferric iron partly by aluminum'. This formula, however, cannot 

 be interpreted rationally; moreover, the considerable amount 

 of hygroscopic water suggests the possibihty that colloidal hy- 

 drates of aluminum and iron are present. Under the micro- 

 scope the material appears to be of high purity; nevertheless in 

 such minutely crystallized material, a gram of which would 

 probably contain more than 6,000,000 crystals, it is quite possible 

 that a considerable amount of impurity might be included and 

 escape detection; nor would such an admixture be surprising, 

 as was pointed out by Hillebrand and Penfield in the original 

 paper on plumbojarosite, where a similar computation was 

 made.^ Possibly the material analyzed represents a mixture con- 

 sisting of a basic sulphate of the composition Pb [Fe (OH)2]4(S04)8 



' Am. Jour. Sci., 4th ser., 14: 215-216. 1902. 



