238 THE CRYSTAL FALLS IRON-BEARING DISTRICT. 



green lualacolite or diopside. This is in roundish grains included in the 

 original green hornblende, which it equals in quantity. 



The orthorlionibic pyroxene occurs in individuals which show fairly 

 good prismatic development, but with rounded terminal faces. The pris- 

 matic cleavage is very well developed. A transverse parting is also com 

 mon. The pyroxene is usually colorless, but in some cases a scarcely 

 noticeable pleochroism was observed, varying from a faint-greenish tinge 

 for rays vibrating parallel to C, to a j^ellow for those parallel to a and 

 Ij. It contains small, dark, streak-like intrusions, some of which under 

 exceptionally favorable conditions are transparent, with a faint-greenish 

 tinge The exit of the bisectrix in basal sections, as well as the parallel 

 extinction, renders it easily distinguishable from the monoclinic pyroxene. 

 The optical angle could not be measured, but was clearly very large, as the 

 hyperbolas passed completely out of the field of view. The orthorhombic 

 pyroxene is evidently enstatite or bronzite, and the pleochroism clearly 

 points to its position near bronzite. A few crystals of rutile and also some 

 of the ihnenite plates, so common in hypersthene, were found occurring in 

 the bronzite. The ihnenite plates are in rather rare irregular patches in the 

 crystals. 



In many cases along the cleavage lines or around the edges of the 

 crystals or along the transverse parting planes are narrow zones of a sec- 

 ondary yellowish-green, finely fibrous, serpentinous mineral. Beyond 

 these zones is a pure white aggregate of secondary talc scales (Fig. B, PI. 

 XXXVIII). Among these scales are a few minute rutile crystals, and also 

 a few black ferruginous specks, these products being probably derived from 

 the inclusions in the bronzite, and the ferruginous material possibly to some 

 extent from the mineral itself. In some cases, instead of the intermediate 

 serpentine zone, the rather rare occurrence is observed of the passage of 

 the bronzite directly into the talc aggregate. 



Olivine. — The determination of the original presence of olivine in the 

 gabbroic rocks is based upon very slight evidence. In some of the sections 

 containing augite almost every individual of this augite has near its center 

 a rounded, very rarely irregular area of yellowish-green fibrous serpentine. 

 These areas are sharply delimited from the surrounding pyroxene, and the 

 conclusion seems wan-anted that it resulted from the alteration of some 

 mineral included in the pyroxene. The only bisilicate found in the rocks 



