Composition:

Petrographic Description:  A hypidiomorphic granular rock composed of 
47% alkali feldspar, 20% plagioclase, 19.7% quartz, 6.3% biotite, 3.3% 
green hornblende, 1.7% colorless augite, and <1% opaque anhedra.  The 
euhedral plagioclase is often complexely zoned and selectively sericitized, 
occasionally showing both albite and Carlsbad twinning.  The alkali feldspar 
anhedra are microcline perthite which also show selective sericitization. 
Brown biotite frequently replaces hornblende marginally; the latter are 
occasionally twinned and commonly contain remnants of colorless augite.  
Minor accessories are coarse sphene, zircon (in biotite), and apatite.  No 
carbonate was seen in thin section, but very weak bands in the spectrum 
indicate a trace amount.

Microprobe Analysis:  The analysis revealed a homogeneous composition 
for the biotite which was titanium and magnesium-rich.  An ilmenite-
magnetite analysis gave 2% ilmenite by weight.  A small amount of 
substitution (approx. 1%) of MgO by FeO was detected in the pyroxene 
while the hornblende analysis showed an equal amount of substitution of 
FeO for MgO.  This analysis shows both augite and hornblende which is 
unusual.  However, the "augite" has very low alumina (approx. 2%) and a 
98% sum, the "hornblende" has over 1% soda and a 97% sum.

Chemical Analysis:
SiO2  64.20
CaO  4.19
TiO2  0.62
Na2O  3.78
Al2O3  15.44
K2O  3.91
Fe2O3  1.38
H2O  0.70
FeO  3.22
P2O5  0.23
MnO  0.07
MgO  2.25
TOTAL  99.99
