CHEMICAL COMPOSITION OF GKANTTE. 19 
Analyses of European granites. 
Si0 2 (silica) TO. 60-74. 82 
ALO3 (alumina) 14.86-16.40 
Fe 2 O a (ferric oxide) _ 0.10- 1.63 
FeO (ferrous oxide) 0.36- 1.64 
MnO (manganese oxide) 1 0.00- 0.48 
MgO (magnesia) 0.23- 1.00 
CaO (lime) 0.89- 2.47 
Na 2 (soda) 3.51- 6.12 
K 2 (potash) , 3.55- 5.10 
Ten analyses, made at the laboratory of the United States Geo- 
logical Survey, of granites from Arizona, California (2), Colorado 
(4), Maryland, Michigan, and Montana, show the following ranges: a 
Analyses of American granites. 
Si0 2 (silica) 66.68-77.68 
ALO3 (alumina) 11.63-16.38 
Fe 2 (), (ferric oxide) 0.00-1.66 
FeO (ferrous oxide) ____ 0.09- 3.32 
MgO (magnesia) 0.04-2.19 
CaO (lime) 0.12-4.89 
Na 2 (soda) 2.36-5.16 
K 2 (potash) 1.87-6.5D 
TiO, (titanium dioxide) 0.07-0.45 
P 2 5 (phosphoric acid) : Trace- 0.10 
The average of 21 analyses of even-grained Georgia granites made 
by Watson & yield the following percentages : 
Analyses of Georgia granites. 
Si0 2 (silica) c 69. 97 
A1 2 3 (alumina) 16. 63 
Fe 2 3 (ferric oxide) 1.28 
CaO (lime) T 2. 13 
MgO (magnesia) 0. 55 
Na 2 (soda) . 4. 73 
K 2 (potash) 4. 71 
It should be noted that in all these analyses most of the lime is to 
be attributed to the lime-soda feldspar and nearly all the rest of it to 
apatite (lime phosphate). 
It is of interest to note in this connection that certain Scotch and 
Irish granites contain from 1.6 to 2.8 volumes of gas per volume 
of rock. This gas is inclosed in microscopic cavities within the 
minerals, and in the Scotch granite consists of carbon, oxygen, 
a See Bull. U. S. Geol. Survey No. 228, p. 54, analysis D ; p. 107. analysis D ; p. 231, 
analysis A; p. 282, analysis A; p. 185, analysis B; p. 161, analyses A, C, F; p. 78, 
analysis A ; p. 145, analysis C. 
6 Watson, Thomas L., Bull. Georgia Geol. Survey No. 9-A, 1902, p. 241. 
c Extremes 68.38-72.56. 
