IXTEiniEniATE ClfAKACTER OF APPALACHIAN GRANITES 



23 



As calculated the range in plagioclase molecules is from intermediate 

 to very acid oligoclase (AbjAnj to AbsAn^). 



Classification. — Total feldspar ranges from 53.03 per cent, to 73.40 

 per cent., with the ratio of potassic feldspar to sodic-lime feldspar less than 

 1 to 2, except in I where plagioclase is more than double orthoclase. In 

 each case the amount of potassic feldspar is within the limits of the quartz 

 monzonite type, although the minimum is practically reached for this con- 

 stituent in I, II, and III, and their approach to the granodiorite type is 

 close. The CaO and ^0,0 contents of these rocks yield a sodic-lime felds- 

 par too acid in composition to group them with the granodiorites, but in 

 the prevailing (older) classifieation they would be properly called qiiartz 

 monzonites, with stronger granite than quartz diorite affinities. 



The position of the South Carolina rocks in the quantitative classification 

 has been computed, and is as follows : 



Granites of South Carolina. 



The remarkable similarity of the South Carolina rocks is shown in the 

 above tabulation. They fall in the same class, order, and rang (domalkalic), 

 and with the exception of I, which is dosodic, they are in the subrang sodi- 

 potassic, and are called toscanose. I is lassenose. 



Georgia. 



Mineral composition. — The Georgia acid plutonic rocks are prevailingly 

 of the biotite type. Muscovite is frequently associated with biotite, and in 

 several localities, notably Stone Mountain, it greatly exceeds biotite in 

 amount. Hornblende is rare and has not been identified in any of the 

 commercial granites in the State. The principal minerals in the rocks are 

 quartz, orthoclase, microcline, plagioclase (oligoclase chiefly, and some 

 albite), biotite, muscovite, apatite, zircon, and iron oxides. Chlorite and 

 epidote are the most frequent secondary minerals. 



