and Notes on ike Associated Topaz. 107 



I =-602 



Ratio 



PeO _ - 43-17 "600 



MgO 0-10 -002 



MnO 42-05 -592 



Ti0 2 1-71 -02' ** 



Avail. O and O from Fe 2 3 9-18 -574 



Si0 2 1*21 



ALO. .-- 2-53 



92 U-( 



99-95 



The ratio of Fe+Mg: Ti + Mn is -602: '613 or nearly 1 : 1, 

 while the oxygen is almost sufficient to convert the MnO into 

 Mn0 2 as indicated by the ratio MnO : O = -592 : -574. As 

 oxygen was determined perhaps as accurately as any other con- 

 stituent, it seems possible that a small amount of manganese 

 may be present as protoxide, replacing FeO. If enough man- 

 ganese be taken as protoxide to make the ratio of RO to R0 2 

 exactly 1 : 1, the results become : 



Ratio. 



FeO __ 43-17 -600 



MgO .... 0-10 -002^- 



MnO 0-40 -006 



Ti0 o ... 1-71 -02: 



sh 



MnO 41-65 



O 9-18 



Si0 2 1-21 



Al O _ 2-53 



99-95 



The oxygen necessary to convert 41*65 per cent of MnO to 

 Mn0 2 is 9'38, which is only slightly in excess of that actually 

 found in the analysis. It seems therefore probable that the 

 mineral is essentially FeMn0 3 =FeO.MnO Q , in which small 

 quantities of MgO and MnO are isomorphous with FeO and a 

 little TiO Q with Mn0 2 . The mineral is therefore to be regarded 

 as a ferrous salt of manganous acid H 2 Mn0 3 , corresponding to 

 braunite MnMn0 3 , which is supposed to be the manganese salt 

 of the same acid. 



We take pleasure in naming this mineral after Mr. Bixby, 

 who has generously supplied us with material for investigation, 

 and has gone to a great deal of trouble and pains to secure the 

 specimens. 



Topaz. — On the topaz with which bixby ite is associated the 

 following forms were observed : 



