Chemical Composition of Amphibole. 

 Proportion of the radicals and remaining bases : — 



47 



[AI,0(OH),]"0 



|Ai.;o 3 R]"d 



[Ai;0 4 RNaJ"0 

 [Fe",Mn,Mg]0 



CaO " 



Ratios 

 '043 

 •032 

 •097 

 •321 

 •169 



Per cents 



6-5 



4-8 

 14-7 

 48-5 

 25-5 



•662 



100-0 



Except for the added radical the interpretation of this 

 analysis is like that of the previous' ones, and again the residual 

 calcium replaces 25 per cent of the hydrogen of the am phi- 

 bole acid. 



Attention will next be called to some varieties of hornblende 

 which do not conform to the two groups previously considered. 



XI. Basaltic Hornblende from Bilin, Bohemia. — rTo col- 

 lectors, this is probably the best known of all basaltic horn- 

 blendes. It occurs in good sized and well formed crystals, 

 generally showing the forms m (110), b (010), r (011) and p 

 (101), often developed so as to appear like a hexagonal prism 

 with rhombohedral terminations. The material used for 

 analysis was obtained from carefully selected crystals, sent to 

 this laboratory by Mr. Warren M. Foote of Philadelphia. 

 The material used for analysis floated on the heavy solution 

 at the specific gravity 3 - 242 and sank at 3*210, the average 

 being 3*226. The results of the analysis are as follows — 















Per cents of 





I 



II 



Average 



Eatios 





protoxide bases 



SiO„ 

 TiO"„ 



39-88 

 1-70 



40-02 

 1-66 



39-95 



1-68 



•666 

 •021 



-•687 





ai,o, 



17-49 



17-68 



17-58 



•173 ' 



- '218 





FeA 



7-25 



7-25 



7-25 



•045 





FeO 



2-18 







2-18 



•031 * 





4-5 ) 



>■ 55*5 



51-0 ) 



MnO 



trace 







trace 









MgO 



14-14 



14-16 



14-15 



•354 





CaO 



12-07 



11-86 



11-96 



•213 



^-•694 



30-7 ) 



K 2 



1-98 







1-98 



•021 



3-0 [-41-1 



Na o 



3-16 







3-16 



•051 





7-4 j 



H/J 



•55 



•53 



•41 



•023 





3-3 



K 



•03 



— 



•03 



•001 





•1 



Loss at 



110° 





•13 









0=:F„ 



100-46 

 •01 



100-0 



100-45 



