466 WARREN AND POWERS DIAMOND HILL-CUMBERLAND DISTRICT 



I II III 



Feldj^par 48.9 55.6 52.6 



Quartz 33.3 33.3 41.4 



I^^^^^^'^^t^ S.5 )q^ g^ 



Aegirite 7.0 J 



Accessories 2.3 1.5 



Total 100.0 100.0 100.0 



Sp. G 2.73 2.66 



hi lift Illft IV 



SiO. 74.1) 74.86 78.49 73.01 



ALO3 9.3 11.61 9.99 11.23 



Fe203 3.7 2.29 1.94 2.53 



FeO 1.8 1.25 1.18 3.66 



CaO .41 .30 .75 



Na,0 ^0 4.30 3.74 5.56 



K,0 4.2 4.64 3.84 3.66 



Rest 2.5 .81 .81 .88* 



Total 100.0 100.17 100.29 101.28 



I. Mineral coiiipositioii by Rosiwal nieasiirement of the riebeckite-regirite 

 granite of Copper Mine Hill. Rhode Island. United States of America. 



II. Mineral composition of the Quincy, Massachusetts, United States of 

 America. C. H. Warren, Proceedings of the American Academy of Arts and 

 Sciences, volume xlix, number 5, September, 1913. 



III. Mineral composition of the riebeckite-ackmite granite from Dahamis, 

 Insel, Sokotra, Elemente d. Gesteinslehre, 1910, edition, page 86. Calculated 

 fi-om the analysis by the writers. 



Itt. Chemical composition of the Copper Mine Hill granite calculated from I. 



II«. Chemical composition of the Quincy granite corresponding to the min- 

 eral composition shown in II. 



Illrt. Chemical composition of the Sokotra granite corresponding to the 

 mineral composition shown in III. 



IV. Chemical composition of the "Riebeckite-porphyry" by J. H. Perry, Bul- 

 letin of the U. S. Geological Survey, number 311, page 66. 



Tt will be seen from the above table that the gi-anite of C'op|XM- Mine 

 Hill, while about as siliceous as that of Quincy, is less rich in feldspar 

 and considerably higher in riebeckite and oegirite. This depresses the 

 amounts of alumina and alkalies, increasing somewhat the total iron. 

 Compared with number TV, it will be noted that, while there are consider- 

 able differences, the silica values are not far apart : likewise total iron and 

 alkalies. The riebeckite porphyry contains only riebeckite, and therefore 

 ferrous iron should be relatively higher in this rock and lower in the 



• MnO = 0.10» MgO = 0.02, BaO. H2O, etcetera. 



