8 



PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 65 



The deductions amount to quartz 8.86 per cent, moWbdenite 2.17 

 per cent and chalcopyrite 1.91 per cent. 



The fourth analysis, made as a final check on the preceding three 

 was on a powder from which the chalcopyrite had not been removed 

 magnetically. It gave the following results: 



Analysis /^ of benjaminite. 



The recalculated percentages for the several analyses of the ben- 

 aminite are collected and averaged in the following table: 



Average and comparison of recalculated analyses. 



Constituent. 



Lead 



Copper 



Silver 



Bismuth 



Sulphur 



Total 



26. 87 



8. 09 



49. 63 

 15. 41 



100. 00 



23.95 



2.87 



4. 19 



53. 83 



15. 16 



25.25 



6.98 



3. 23 



48.24 



16.30 



100. 00 



100. 00 



24.70 



4.22 



3. 11 



51. 45 



16. 52 



100. 00 



Aver- 

 age. 



25. 18 



4. 69 



3. 51 



50.78 



15.84 



100. 00 



The average column from the above table gives the ratios of the 

 following table: 



Ratios of average analyses. 



The above ratios indicate the formula for the mineral to be Pbj 

 (Ag, Cu)2Bi,So or 2PbS.(Cu, Ag) 28.261,83. The average of the analy- 

 ses is below repeated in comparison with the theoretical percentages 

 and with several related minerals. 



