23(3 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Norm. 



Acmite . 92 



Diopside 2 . 71 

 Hypersthene 1 . 19 

 Magnetite 2.09 

 Ilmenite . 76 



Apatite . 34 



99.37 



K2O + Na^.O 



CaO 



8.01 Femic Minerals 



K.O 

 Na 6 



= > 7 = Range 1 ; peralkalic. 



= .73<|>|; 



Subrange 3; sodipotassic. 

 Liparose. 



The rock is therefore a riebeckite-grano-Uparose. 



In calculating the mineral composition the albite was taken a3 

 AbgsAns, which is as near as it could be determined, and the total 

 amount of feldspar was assumed to be that found by a careful Rosival 

 measurement made on two thin-sections. The small amount of cal- 

 cite and limonite were disregarded, but a part of the water above 110° 

 was used in the proportion in which it was known to be present in 

 the Riebeckite hornblende of the pegmatites ^^ which optically ap- 

 pears to be identical with that in the fine-granite. 



The results are as follows : • — • 



Calculated. 



Quartz 



Albite AbgsAns 

 Microcline 

 Hornblende 

 Magnetite | 

 Ilmenite J 

 Zircon 

 Apatite 



23.3 

 36.93 

 29.47 

 8.41 



1.46 



.10 

 .34 



Ratios. 



= 2.84 



1.25 



10.3 



100.00 



10.7 



100.00 



Albite = 55.6 

 Microcline = 44.4 



Microperthite = 100.00 



The percent of the molecules Na2Fe2Si40i2 and (R'2R")4Si40i2 

 in the hornblende were found to be 44 and 56% respectively. In the 

 pegmatite Riebeckite these were, 42 and 58%, which are in good agree- 

 ment with those from the granite, and indicate the close similarity 

 of the two hornblendes which was inferred from their optical charac- 

 ters. 



Compared with the coarse-granite (4), we note 3.4%, less silica; 

 1.1% more alumina; 0.5% higher total iron oxides, Ijut with ferrous 



31 Warren & Palache, loc. cit., p. 154. 



