MARYLAND GEOLOGICAL SURVEY 133 



CHEMICAL COMPOSITION. 



Pyroxenite (websterite) from Oakwood. 



RECALCULATION. 



Hypersthene 43.72 



Diallage 55.97 



Misc 79 



Si0 2 53.21 



A1 2 3 1.94 



Fe 2 3 1.44 



FeO 7.92 



MgO 20.78 



CaO 13.12 100.48 



Na 2 11 



K 2 07 



H 2 + 87 



H 2 0- 14 



C0 2 10 



Ti0 2 26 



Zr0 2 trace 



P 2 5 « 



CI., F undet. 



FeSa 1 03 (.02 S.) 2 



Cr a 8 20 



NiO, Co O 03 



MnO 22 



BaO none 



SrO 



Li 2 trace 



V 9 0, 03 



Total 100.47 



Analysis made by W. F. Hillebrand, of the United States Geological Survey. 

 Amer. Geol., vol. xxviii, 1901, p. 159. 



The specimen that was analyzed was a fresh websterite, containing 

 only hypersthene and diallage. 



The recalculation shows the relative proportions of these con- 

 stituents. 



PERIDOTITE. 



This type is, like the pyroxenite, found associated with the serpen- 

 tine, and as included bodies and dikes within the gabbro belt. 



The largest body, one mile southwest of Sylmar, exposes a peri- 

 dotite largely altered to serpentine, One and one-half miles north 

 of Harrisville, there occurs another area of peridotite. 



1 Sulphur is calculated as FeS 2 , but exists as pyrrhotite or other sulphide soluble 

 in HC1. 



2 Perhaps mainly pyrrhotite. 



