Bradley — Composition of the Mineral Warwickite. 183 



This would point to B 2 3 . Ti0 2 . 3(Mg, Fe)0 as the formula 

 for the mineral. Since, however, a glassy green spinel is so 

 intimately associated with the warwickite and its separation 

 from it, both on account of its closely similar specific gravity, 

 and because under the microscope it assumes an almost metallic 

 appearance, it is thought reasonable to assign the 2*91 per cent 

 of A1 2 3 found to its presence in the material analyzed. This 

 assumption would necessitate the subtraction of an equivalent 

 amount of MgO as required by the formula MgO . A1 2 3 . 

 Qualitative and quantitative tests on this spinel have proven it 

 to correspond essentially to the variety known as chlorospinel, 

 in which a little of the A1 2 3 is replaced by Fe 2 3 . In this 

 particular spinel there was found 8*92 per cent of Fe 2 3 , and 

 corrections for this isomorphous Fe 2 3 introduced into the 

 warwickite analysis by means of this spinel have been accord- 

 ingly made. 



The presence of magnetite associated with the warwickite 

 was proven by testing the impure material by the ordinary 

 magnet. If, as is possible, it was intimately mingled with the 

 warwickite it would be difficult to entirely separate it, as the 

 warwickite itself is attracted easily by the electro-magnet. It 

 seems reasonable therefore to assume that the greater part of 

 the Fe 2 3 found was contained in magnetite, and that an 

 equivalent amount of FeO to correspond to FeO . Fe 2 3 should 

 be deducted from the analysis. Treating the analysis in this 

 way we have the following results : 



Eatio 



1 



1-090 

 3-134 













Calculated 





Average 





Spinel 



Magnetite 



III 



to 100 





BA 



21-29 







21-29 



23-87 



•341 



Ti0 2 



24-86 







24-86 



27-87 



•347 



Si0 2 



1-39 







' 1-39 



1-56 



•025 



MgO 



35'7l 



— 1-26 





34-45 



38-63 



•957 



FeO 



9-15 





— 1-95 



7-20 



8-07 



•112 



Fe 2 3 



4-76 



— '42 



— 4-34 









A1 2 3 



2-91 



— 2-91 





89-19 









100-07 



100-00 





The ratios from the corrected analysis yield B 2 3 . TiO a . 

 3i Mg, Fe)0 as before, but with sharper agreement between the 

 theoretical and derived numbers. The formula for warwickite 

 can then be written, 



(Mg,Fe) 3 TiB 2 8 



which could be developed into a symmetrical structural for- 

 mula as follows : — 



