KNOPF : PLUMBOJAROSITE FROM NEVADA 501 



to which it can be referred was recognized under the micro- 

 scope, the siHca, titania, the minor constituents, and the precious 

 metals are regarded as impurities; the analysis was recalculated 

 to 100 per cent. The molecular ratios were then obtained, the 

 CuO was used to determine the amount of beaverite, and the 

 other constituents were allotted in accordance with the formula 

 CuOPbOFe2032S034H20; the remaining PbO together with the 

 alkalis, was used to determine the amount of plumbojarosite 

 according to the formula Pb03Fe2034S036H20. 



This summation of the calculated mineral composition to 100.59 

 strongly confirms the microscopic diagnosis that the analyzed 

 material is a mixture of plumbojarosite and beaverite. 



Vegasite, a newly recognized basic lead-ferric sulphate. A straw 

 colored ocherous mineral, forming relatively pure lumps up to 

 several inches in size, occurs at the Rosella prospect, which is 

 situated several hundred feet north of the Boss mine. Quali- 

 tatively it gives the reactions of plumbojarosite, but quantitative 

 data show apparently that it is a new mineral. It differs from 

 plumbojarosite in specific gravity, refractive indices, and molec- 

 ular ratios. 



Under the highest power of the microscope the mineral is 

 found to be exceedingly fine grained. It is well crystalhzed, 

 however, showing principally minute fibers; but scattered among 

 these are also a considerable number of six-sided plates, apparently 

 belonging to the hexagonal system. The plates are all under 

 0.01 mm. in diameter and range down to 0.002 mm. By causing 

 the fibers to move with a rotatory motion through the liquid in 

 which they are immersed, it can be seen that the fibers represent 

 the edges of the hexagonal plates. 



The plates are isotropic; the fibers are strongly birefringent 

 and give parallel extinction. The mineral is therefore probably 

 uniaxial. The fibrous sections are markedly pleochroic, ranging 

 from brownish yellow to pale yellow, the absorption being e>co. 

 The indices as determined by the immersion method are: 

 € = 1.82 ± 0.01 and co = 1.755 ± 0.002; the mineral is therefore 

 optically positive. 



