212 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



the fresh rock has been attacked more than the altered rock. Complete analyses 

 of the mine waters show chiefly carbonates of lime and magnesia in about equal 

 proportions, next, sulphate of magnesia and silica, a smaller amount of carbonate 

 of soda, about one-tenth as much carbonate of potash as soda, small amounts of 

 sodium chloride, and very small proportions of alumina and ferric oxide." 



MEANING OF ADULARIA AND ALBITE AS GANGUE MINERALS. 



While it might be inferred from this that ordinary waters, .even those 

 containing a large amount of soda and little or no potash, tend to produce potash 

 minerals in veins and owe their composition to the leaching out of the soda while 

 the potash is left behind, the fact remains that potash feldspar is contained, so far 

 as known, only in a relatively limited number of veins. 



Soda feldspar or albite, a mineral as easily formed in the wet way as orthoclase, 

 occurs in a number of other veins and in rocks as the result of the alteration of 

 soda-lime feldspars, and, what is more interesting, of potash feldspars. Dr. G. L. 

 Gentil* has shown that in the granites of the Tofna basin in Algeria the soda-lime 

 feldspars have been largely transformed into albite, and the same phenomenon has 

 been described by other authors. On St. Gothard and other places in the Alps 

 albite has been described as pseudomorphous after adularia, and as occurring in 

 porous aggregates of fine c^-stals in the form of the original potash-feldspar 

 crystal. Comparative analyses of the feldspar's various phases of alteration show 

 that the original adularia contains very little soda and the resultant albite no 

 potash. Bischof <" explains this process of pseudomorphism as a decomposition of 

 the original adularia by waters into a perfectly soda-free adularia and a potash-free 

 albite. The potash, silica, alumina, and lime of the adularia were dissolved and 

 carried away, leaving the albite; in some cases the albite substance seems to have 

 been concentrated. Bischof suggests d that in some cases part of the adularia 

 has been transformed into albite by replacement. Also in localities in the 

 Riesengebirge in Austria small fresh albite crystals were observed in several 

 cases upon altered orthoclase, which was in part altered to muscovite/ Bischof 

 and Rose agree that the explanation of this is that the soda-feldspar has been 

 abstracted while the potash feldspar remains. Bischof remarks, " Such opposite 

 effects-'' presuppose beyond question, if not opposite, certainly different causes, i. e., 

 different substances in solution in the waters." 



a BecKer. G. F., Mon., U. 8. Geol. Survey, vol. 3, p. 162. 

 '- 1 i.-nlil. O. L., Review In Am. Geol., Apr., 1903, p. 264. 

 oBlnchof, Gustav, Chemische Geologic, vol. 2, p. 409. 

 dOp. clt., p. 412. 

 Op. cit., pp. 406, 407, 412. 



/That In, In one case the adularia molecule was dissolved out, the albite molecule being insoluble; in the other the 

 albite molecule was diwolved out, while the adularia molecule was insoluble. 



