Composition:

Petrographic Description:  The granitoid rocks of the Corona stock are
typically hypidiomorphic granular.  The quartz is anhedral with moderate to
strong undulose extinction, plagioclase forms subhedra with strong normal
compositional zoning, the orthoclase is perthitic and the biotite is partly
chloritized.  The modes for this sample are:  34.8% plagioclase, 34.3%
potassium feldspar, 28.1% quartz, and 2.4% biotite.  No carbonate was seen 
in thin section, but very weak carbonate features in the powder spectrum 
indicate a trace amount, as does the chemical analysis.

Microprobe Analysis:  Compositionally these zoned plagioclases contained 
15% anorthite (oligoclase) in the rims of the feldspars.

Chemical Analysis:
SiO2  73.9
CaO  1.0
TiO2  1.1
Na2O  3.9
Al2O3  13.3
K2O  4.5
Fe2O3  0.58
H2O  0.31
FeO  0.56
P2O5  0.04
MnO  0.04
CO2  <0.05
MgO  0.33
TOTAL  99.46
