36 COLORADO FERBERITE AND THE WOLFRAMITE SERIES. 



CONSIDERATION OF THE ANALYSES. 



The collection of analyses just given indicates an essentially 

 complete series of mixtures of manganese and iron tungstates ranging 

 from pure manganese tungstate to pure iron tungstate, with the 

 possible number of members limited only by the number of speci- 

 mens analyzed and by the accuracy of the determinations. The 

 series is analogous to those of the plagioclase feldspars and the 

 columbite-tantalite group. The greatest difference between consecu- 

 tive analyses in either hiibnerite or wolframite molecules is 5.5 per 

 cent, which is found between the wolframites from Lost River, 

 Alaska (No. 34), and Vilate, France (No. 35), which contain, respec- 

 tively, as recalculated, 56.7 per cent and 51.2 per cent MnWO 4 , but 

 there can be little doubt that analyses of other specimens from these 

 or other localities would fall within the gap. It is also probable that 

 if the exact quantity of iron and manganese combined as tungstates 

 were known, the results would be considerably different. Most 

 writers on the subject have treated the wolframites as definite com- 

 pounds of FeWO 4 and MnWO 4 , bearing relations to each other which 

 could be expressed by small whole numbers, but this does not seem 

 to be borne out by the analyses. Groups of analyses of wolframites 

 from Zinnwald, from the Boulder district, and from the Black Hills, 

 all smah 1 areas, show a very considerable variation in the ratio of 

 iron and manganese bearing molecules. Those from Zinnwald range 

 from 77.0 per cent to 60.2 per cent MnWO 4 , and those from Boulder 

 County range from 36.2 per cent to 0.4 per cent MnWO 4 . In some 

 crystals of hubnerite a considerable variation in color, probably due 

 to difference in composition of different zones, can be seen. Were 

 it not for the black color of each part, a zonal growth similar to 

 that of porphyritic plagioclase feldspars could probably be observed in 

 many wolframite crystals. (See PL XIII, p. 30.) As stated in another 

 place by W. T. Schaller, no difference in crystal form can be noticed 

 between the two ends of the series. If there were a series of definite 

 compounds between the two end members, some expression of the fact 

 would probably be found in the facial angles. 



Attention is called to the number of wolframites whose analyses 

 show the presence of tantalum and columbium. It is probable 

 that in some analyses, particularly the earlier ones, other substances 

 have been determined as these elements, and in other analyses they 

 have not been recognized or determined when present. Dr. Eberhard 

 showed spectroscopically (p. 18) that columbium was present in a 

 specimen of Boulder County ferberite, but he made no test for 

 tantalum. Where one element is present, however, the other is 

 almost sure also to be there. 



