498 KNOPF: PLUMBOJAROSITE FROM NEVADA 



the Red Warrior mine, Beaver County, Utah.'* The results of the 

 measurements for sodium hght are: 



Refractive indices of -pi umbo jaro site 



* This unpublished determination, made by E. S. Larsen (on the type 

 material originally analyzed by Hillebrand), has been added for the sake of 

 completeness. 



In regard to this material Wright states that "The differences 

 in refractive indices between the different samples are not great 

 and within the limits of error, which I have put purposely large 

 because of the character of the material. Of the three samples 

 that from the Red Warrior mine seemed to contain the most 

 impurity in the form of opaque inclusions scattered through the 

 crystals. The sample from Nevada is much finer grained than 

 the other two." 



Chemical composition. An analysis of the plumbojarosite from 

 the Boss mine has been made by Dr. R. C. Wells. This is given 

 in the following table together with the analysis of the Utah 

 material whose indices were determined by Wright. For 

 comparison the composition calculated from the formula 

 Pb03Fe2034S036H20 is also given. 



The silica and titania shown by the analysis represent a me- 

 chanical admixture of quartz and octahedrite crystals, which 

 remain as a residue after dissolving the mineral in hydrochloric 

 acid; the precious metals are present in minute metallic par- 

 ticles. In spite of the apparent homogeneity of the analyzed 

 material and its optical identity with the very pure mineral 

 from American Fork and Beaver County, the material from the 

 Boss mine shows a divergence in chemical composition from the 

 other analyzed specimens, the most important being the lower 



■^ Butler, B. S., and Schaller, W. T., Some minerals from Beaver County, 

 Utah. Am. Jour. Sci., 4th Ser., 32:422. 1931. 



