COMPOSITION OF FERBERITE AND OTHER MEMBERS OF SERIES. 21 



The analyses have all been recalculated in order to bring them to 

 a common basis on which they can properly be compared. 



To do this it has been assumed that the theoretically pure members 

 of the wolframite series contain only the hubnerite molecule, MnWO 4 ; 

 the ferberite molecule, FeWO 4 ; or a combination of the two mole- 

 cules. All analyses have been reduced to these simple forms. 



As scheelite, the calcium tungstate,. CaWO 4 , almost universally 

 accompanies the wolframites, the lime indicated in the analyses has 

 been considered to be a component of scheelite unless data given 

 with the analysis showed it to belong to some other mineral, such as 

 fluorite. As the CaO is an impurity, it has therefore ordinarily been 

 satisfied with WO 3 and then discarded with all items other than FeO, 

 MnO, and WO 3 . Of course, this scheme probably leads to error in 

 certain of the analyses, as the lime in some may be derived from 

 other sources than scheelite, but these sources can not all be known, 

 and as a general rule the process just described seems warranted. 

 As applied to the Boulder field in particular there can be little objec- 

 iion ; as lime-bearing minerals other than scheelite are uncommon. 

 Calciferous feldspars seem to occur in very few places, calcite is rare, 

 and no other lime minerals have been noted in the veins. 



The analyses have been arranged in a series of decreasing MnWO 4 

 and increasing FeWO 4 content, so that the series begins with the 

 hubnerites and ends with the ferberites. This has determined the 

 order of calculation, for the natural procedure has been 



the MnO with WO 3 and then to combine the remaining WO 3 with 

 so much of the FeO as it would take up. Arbitrary or casual reasons 

 are not the only bases for this mode of calculation, however, for man- 

 ganese is much less common as an impurity in wolframites than is iron. 



The quantity of MnWO 4 and FeWO 4 obtained as a result of the 

 operations has then been treated as the theoretically pure wolframite 

 present in the substance analyzed, all other substances present being 

 considered as impurities. From the theoretical wolframite as a basis 

 have been computed the percentages of WO 3 , FeO, MnO, FeWO 4 , and 

 MnWO 4 of which it is composed. 



In making the calculations the following atomic values and molec- 

 ular ratios have been used : 



Atomic weight. Molecular ratio. 



Calcium 40 



Iron 56 



Manganese 55 



Oxygen 16 



Tungsten 184 



The values of the atomic weights are used only to the nearest 

 integer and the ratios to the second decimal. These values are as 



WO. 232 



W0 8 232 



FeO ~ 72 3> 22 



wo ' ^.. 



