Chemical Composition of A niphibole. 



49 



Of the two interpretations the latter is probably the sim- 

 pler and brings the residual calcium nearer to 25 per cent as 

 in the previous analysis. It should be pointed out also that 

 if the basic alumo-radical used in this analysis is taken by itself 

 and combined with its equivalent of silica, the result becomes 

 ■(Na !! ,Ca)(Fe,Mg)Alj3i 2 J2 , analogous in type to the basic 

 jalumo-silicate molecule of Tschermak, page 24. The essential 

 difference in this particular case between Tschermak's theory 

 and the present one is that, according to the former a definite 

 basic alumo-silicate molecule is regarded as isomorphous with 

 Ca(Fe,Mg) 3 Si 4 12 . 



XII. Hornblende from Grenville township, Quebec, Canada. 

 — This hornblende is very unusual on account of the large 

 amounts of alumina and fluorine it contains and the low per- 

 centages of iron, a combination not often met with. It has been 

 analyzed by Prof. B. J. Harrington,* who has kindly sent on 

 material for study, and by R. A. A. Johnston. f The color of the 

 mineral is a light brown, with somewhat of a reddish tone : it is 

 unusually transparent and shows a perfect prismatic cleavage. 

 The specific gravity as given by Harrington is 3'll0. The new 

 analysis by Stanley, from which the ratio is calculated, confirms 

 the results of the earlier analyses. 



Per cents of 

 Harrington Johnston Stanley Eatios , protoxide bases 



Si0 2 



45-50 



46 09 



45-79 



763 



Ti0 2 



•68 



undet. 



1-20 



015 



A1 2 3 



12-25 



12-93 



11-37 



112 



Fe 2 3 



•28 



•79 



•42 



003 



FeO 



■15 



none 



•42 



006 



MnO 



•11 



•36 



•39 



006 



MgO 



20-63 



20-82 



21-11 



528 



€aO 



13-31 



1291 



12-71 



227 



K 2 



1-76 



1-84 



1-69 



018 



Na 2 



2-76 



2-36 



2-51 



040 



H 2 



•40 



•66 



•67 



037 



F a 



2-80 



2-84 



2-76 



072 





101-23 



101-60 



101-06 





= F ; 



1-17 



1-19 



1-16 





y 



778 

 •778 



•115 



y-934 



565 ysl-o 



•6 



•6 



56-5 



24-3 



2-0 



4-2 



3-9 



7-9 



100-0 



57-7 



30-5 



100'06 100-41 



99-90 



It may be noted first that with a sesquioxide quotient of 

 •115 the ratio of Si0 2 :RO-f-F 2 is as 1 : 1-20, which is not 

 exactly in accord with the results obtained from analyses YII 

 *This Journal, xv, 392, 1903. f Geol. Sur. of Can., vol. xiii. 



Am. Jour. Sci. — Fourth Series, Vol. XXIII, No. 133. — January, 1907. 

 4 



