Chemical Composition of Amjphibole. 



39 



and also into actinolite. The names are not very characteristic 

 nor significant, and perhaps the designation of these various 

 varieties as hornblende is more satisfactory than the attempt to 

 make use of several names. As will be shown, the hornblendes 

 are characterized by having a somewhat different ratio of Si0 2 

 to the protoxide bases than that determined for tremolite and 

 actinolite. 



VII. Hornblende from Renfrew, Ontario, A 



Canada. — The crystal analyzed was of an 

 unusually black color and brilliant luster, 

 showing' the forms a (100), b (010), m (110), 

 r (011) and i (031), figure 4. The specimen 

 is No. 487 of the Brush Collection. Frag- 

 ments used for analysis floated at 3*330 and 

 sank at 2*249, the mean specific gravity being 

 3*290. 'The results of the analysis follow : — 



< 



r 



m 



b 



[i 



a 



— yj— 



b 













I 



II 



Average Eatios 



Si0 o 



43*92 



43*60 



43-76 



■728 



Tio; 



•78 







•78 



•010 



A1„0 3 



8*35 



8*31 



8-33 



•081 



FeA 



6*99 



' 6*80 



6*90 



•043 



FeO 



10*40 



10*54 



10*47 



•146 



MnO 



•50 







•50 



•007 



MgO 



12*67 



12*60 



12*63 



•315 



CaO 



9*86 



9*82 



9-84 



•176 



K„0 



1*28 







1-28 



•014 



Na,0 



3*43 





3-43 



•055 



H 2 



. *75 



•55 



•65 



•036 



f; 



1*82 







1-82 



•048 



Loss at 



110° 





•10 







100-49 









= F 2 



•76 





Per cents of 

 protoxide bases 



•738 



•124 



J>-797 



18 







39 



2 2 

 1 



3 



9 \ 

 5 



s y 



9 

 5 



100-0 



99-73 



VIII. Hornblende from .Edenvitte, Orange Co., New York. — 

 Crystals from this locality occur large and of a black color, very 

 closely resembling those from Renfrew ; the forms also, b, m, 

 r and i are frequently developed as in figure 4. The material 

 used for analysis floated at 3*291 and sank at 3*278, the average 

 being 3*285. The results of the analysis follow : 



