LARSEN AND HUNTER." MELILITE 477 



has been found in all stages of this alteration, which is no doubt 

 due to the action of water solutions, probably hot solutions from 

 the intruding pyroxenite magnia. 



PEROFSKITE 



The relatively rare mineral, perofskite, is an abundant con- 

 stituent of the melilite rock, the pyroxenite, and the ijolite. It 

 is one of the chief constituents of the magmatic segregations of 

 "iron ore" which are abundant in the pyroxenite. These segre- 

 gations are made up of about equal amounts of magnetite and 

 perofskite with varying amounts of apatite and biotite. So far 

 as observed there is no ilmenite present. Singlewald^ and Brun- 

 ton^ have not distinguished this type of iron ore from the more 

 common ilmenite-magnetite ore. 



In the melilite rock the perofskite, which is commonly in grains 

 or octahedral crystals, forms several per cent of the rock, and 

 Ideally is next to melilite in abundance. The larger crystals are 

 several millimeters across. 



The perofskite is iron black in color and has a sub-metallic 

 luster approaching adamantine. In appearance it differs from 

 magnetite, chiefly in luster, and the two minerals are difficult to 

 distinguish megascopically except by the lack of magnetism in 

 the perofskite. It is even more difficult to distinguish from some 

 of the titaniferous garnet. 



In thin sections the perofskite is weakly birefracting and shows 

 a complex of polysynthetic twin lamellae resembling the grating 

 of microcline or less often the albite and pericline twins of plagio- 

 clase. It is translucent and, in transmitted light, is Saccardos 

 umber^ in color and is perceptibly pleochroic with the absorption 



' Singlewald, J. T., The iron ore deposits of the CeboUa District, Gunnison 

 County, Colorado: Econ. Geol., 7: 560. 1912. 



^ Brunton, S., Some notes on titaniferous magnetite. Econ. Geol., 8: 677. 

 1913. Iron stained plagioclase is mentioned as a constituent of the iron ore from 

 the Cebollite District. We have found no plagioclase in the ore but some of the 

 perofskite shows polysynthetic twinning somewhat resembling that ot plagio- 

 clase and might have been mistaken for an iron stained plagioclase. 



* Color 17" k of Ridgway's "Color standards and nomenclature," 1912, Wash- 

 ington, D. C. 



