Composition:

Petrographic Description:  A sample of typical diabasic texture, with 
euhedral to subhedral plagioclase laths showing albite twinning and zoning 
(normal and oscillatory).  The plagioclase makes up 48% of the rock.  The 
anhedral pyroxenes (26% orthopyroxene, 22% clinopyroxene) commonly 
show exsolution lamellae, and the clinopyroxenes are occasionally twinned 
and frequently show "herringbone" exsolution.  Minor biotite (0.5%) 
replaces some pyroxenemarginally, while opaque phases constitute about 
2% of the sample.

Microprobe Analysis:  The feldspar composition was that of labradorite,
ranging from An65 to An69.  The hypersthene, according to one analysis, 
had 40 mol % ferrosilite.  The augite was homogeneous with about 20% 
FeO, 40% MgO, and 40% CaO.  An analysis of ilmenite indicated about 1% 
MgO.

Chemical Analysis:
SiO2  52.41
CaO  11.70
TiO2  0.94
Na2O  1.64
Al2O3  13.11
K2O  0.47
Fe2O3  1.35
H2O  0.80
FeO  8.34
P2O5  0.07
MnO  0.17
MgO  9.36
TOTAL  100.3
