A PYRRHOTITIC PERIDOTITE FROM KNOX COUNTY, 

 MAINE^— A SULPHIDE ORE OF IGNEOUS ORIGIN 



EDSON S. BASTIN 

 Washington, D. C. 



The rock here described, though of slight areal extent, is of rather 

 unusual interest as a representative of a little-known type of sulphide 

 ores consolidated from a molten magma, and also as the first-described 

 representative of subclass 2 of the perfemane class (class V) of the 

 quantitative system of classification, all of the extremely basic rocks 

 thus far described falling in subclass i, perfemane, of this class. 

 The rock also shows beautiful examples of reaction rims of hornblende 

 between plagioclase feldspar and olivine, an alteration to which little 

 reference has been made in petrographic literature. 



Location and geologic occurrence. — The rock here described occurs 

 on the farm of Mr. Charles A. Millers, about three-fourths of a mile 

 southwest of the village of East Union in the town of Union, Kjiox 

 County, Maine. It constitutes a single outcrop about forty to fifty 

 feet across. The rock disintegrates rapidly, and the partly disinte- 

 grated material has been excavated to some extent for use in improv- 

 ing the roads. All of the present surfaces are rusty, and a number 

 of well-rounded bowlders of disintegration which have withstood 

 weathering longer than other portions lie partially imbedded in 

 the gravelly disintegrated material. The rock is extremely tough 

 and resistant under the hammer. 



In the woods, about one-half mile southeast of the outcrop de- 

 scribed above, a small prospect pit has been dug in loose ferruginous 

 material, which probably passes below into rock similar to that on 

 the Millers farm. 



The above-mentioned localities lie within the area of the Rockland 

 quadrangle, near its western border. The rocks of the region are 

 regionally metamorphosed sediments probably of Cambro-Ordovician 

 age, which have been intruded and further metamorphosed by granitic 

 rocks. The peridotite here described is in all probability intrusive 



I Published with the permission of the director of the U. S. Geological Survey. 



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