:oo 



W. E. Ford — Chemical Composition of Axinite. 



II. Axinite from Bourg d'Oisans, by Whitfield. 







Eatio. 





According to 

 Whitfield. 





According to 

 new formula. 



Si0 9 ..._. 



41*53 



•692 -S- 



•069 



= 10-00 or 



10-00 



^•086 



= 8-00 or 8-00 



B.O, - - 



4-02 



•066 





= -95 



1-00 





= -76 1-00 



A1 2 3 .. 

 Fe 2 3 __ 



17-90 

 3-90 



' m l'197 

 •024 \ iy/ 





= 2-85 



3-00 i 





= 2-29 2-00 



FeO ... 



4-02 



•056^ 

 •053 I 

 •386 !>' 513 

 •018 1 

 •120 







1 



8-00 1 

 | 







MnO... 



CaO ... 

 MgO... 



3-79 

 21-66 



•74 





= 7-43 





= 7-36 7-00 



H 2 0...- 



2-16 





1-74 



2-00 J 







100-32 



Without question Whitfield's determinations of B 2 3 are too 

 low, and they would naturally be so if precautions were not 

 taken to extract all of that constituent by repeated fusions 

 with sodium carbonate and addition of silica. 



Conclusion. — As the result of the foregoing investigation it 

 would seem well established that axinite is a silicate in which 

 the boron and the bivalent and trivalent bases are present in 

 definite proportions. Expressed as an orthosilicate the formula 

 is R^I^^B^SiO^. The bases are chiefly calcium and alu- 

 minum, the Ca being always replaced in part by varying 

 amounts of Mn, Fe, Mg and H 2 , while a little Fe is isomor- 

 phous with the Al. A little hydrogen seems to be an unfail- 

 ing constituent of axinite, and expressed as H 2 0, the amount 

 is remarkably constant in the analyses. As far as observed 

 however, water is never present in sufficient quantity to satisfy 

 the formula of Rammelsberg, and it seems best to regard it as 

 basic, a role which it often plays. 



Note on the crystals of axinite from Obira, Japan. — Two 

 distinct types of crystals of axinite come from this locality. 

 The first to be described is that of the material used in making 

 Analysis No. II of this article. These crystals do not occur in 

 separate individuals but in groups, made up of numerous crys- 

 tals in nearly parallel position, rounding into one another. It 

 is only at the edges of the groups that distinct crystal faces are 

 seen. Measurements were made of these faces, and while as a 

 rule the reflections obtained were poor, the following common 

 forms were readily identified, developed about as represented 

 by fig. 1: I (010),' m (110), M (110), w (130), s (201), x (111) 

 and r (111). In reality the crystals are so grouped that only 

 the faces shown in the upper right hand portion of the figure 

 are to be seen. A characteristic feature of the crystals is a 

 tendency for the x and s faces to round into one another, fig. 

 2 being an attempt to represent this. Still another tendency 



