Composition:

Petrographic Description:  A uniformly-grained aggregate of chiefly 
euhedral to subhedral plagioclase laths and anhedral pyroxenes in a classic 
diabasic texture.  The plagioclase frequently shows oscillatory zoning, less 
commonly normal zoning.  The augite usually contains exsolution phases 
and is occasionally twinned.  Minor biotite replaces some pyroxenes 
marginally.  Modal analysis gave:  46% feldspar, 35% clinopyroxene, 14% 
orthopyroxene, 2% opaques and 1.2% biotite.

Microprobe Analysis:  The analysis revealed the feldspar composition to 
range from labradorite to bytownite (An56 to An72).  Individual grains often 
varied in composition between labradorite and that of bytownite due to 
zoning.  The augite frequently showed complex substitutional relationships 
among the divalent cations FeO, MgO, and CaO, probably a result of 
exsolution.  One augite grain probed showed hypersthene exsolved from 
salite, while another grain gave a mixture of magnesian pigeonite and salite.  
The orthopyroxene grains (not the exsolved phases) proved to be 
hypersthene, one of which was 33 mol % ferrosilite.  Other phases probed 
were ilmenite and phlogopite.

Chemical Analysis:
SiO2  52.54
CaO  11.74
TiO2  0.86
Na2O  1.61
Al2O3  12.82
K2O  0.45
Fe2O3  1.16
H2O  0.98
FeO  8.44
P2O5  0.09
MnO  0.17
MgO  9.81
TOTAL  100.6
