208 BROWN & HERON: GEOLOGY AND ORE DEPOSITS OF TAVOY 



Hiibnerite, manganese tungstate, MnWO,. 



Wolframite, iron-manganese tungstate, (FeMn)W0 4 . 



Sclieelite, calcium tungstate, CaWO,. 



Stolzite, lead tungstate, PbW0 4 . 



Ra spite, lead tungstate, PbW0 4 . 



Cuprotungstite, hydrous copper tungstate, CuW0 4 ,2H 2 0. 



Tungstite, hydrous tungsten tri oxide, WO a ,H 2 0. 



Ferritungstite, hydrous iron-tungsten oxide, Fe 2 8 ,W0 8 ,6H 2 0. 



The iron and manganese tungstates form a good example of an 

 isomorphous series. The two theoretical end products are ferberite, 

 the tungstate of iron, and hiibnerite, the tungstate of manganese. 

 Mineralogists have attempted to show that the various mixtures 

 of theso two tungstates found in nature, bear a definite ratio as 

 regards the proportion of the molecules of the two compounds present, 

 but it has been demonstrated that the two may mix in any propor- 

 tion and that the series is composed of an infinite number of members. 

 It has been suggested therefore that arbitrary divisions shall be made 

 as follows : — 



Ferberite should be considered an iron tungstate, (FeWO ), 

 contaminated by not more than 20 per cent. Mn WO + , a proportion 

 equivalent to 4-69 per cent. MnO, or 363 per cent. Mn, in the pure 

 tungsten mineral. 



Hiibnerite should be considered a manganese tungstate, (Mn 

 WOJ, contaminated by not more than 20 per cent. Fe WO p a propor- 

 tion equivalent to 4-74 per cent. FeO, or 3-G9 per cent. Fe. Wolf- 

 ramite should cover the ground between the limits indicated above. 

 That is, it should be considered a mixture of iron and manganese 

 tungstates containing not less than 20 per cent, and not more than 

 80 per cent, of either. 1 



As the exact chemical determinations entailed by this classifi- 

 cation have not been made in the case of the Tavoy mineral, the 

 general term wolfram is used to cover all varieties in these pages. 

 Certain Tavoy specimens which appeared to possess the charac- 

 teristics of hiibnerite were analysed, but were found to come within 

 the wolframite limits of the above classification. It will probably 

 be found that this holds good for most of the material from the district. 



•Hess, United States Geological Survey. Bull., 652. 



