ART. 18 MINEEALS OF ITALIAN" MOUNTAIlSr CEOSS AND SHANNON 5 



nate. Biotite and hornblende occur rather in grains than in leaves 

 or prisms and their even distribution is a marked feature. Mag- 

 netite, apatite, titanite, zircon, pyrite, and allanite are the acces- 

 sories in decreasing order of abundance. Honey-yellow titanite 

 grains or crystals are characteristic but allanite is very rare. 



Plagioclase is the most abundant constituent, occurring in stout 

 little prisms often with an irregular fringe of oriented orthoclase. 

 Zonal variation is usual, the center being Abg An^ is some crystals 

 determined and the outer zones ranging to oligoclase. Orthoclase 

 and quartz play similar roles, each occuring commonly in anhedral 

 grains but not infrequently serving as matrix for other mineral 

 particles in irregular patches of microscopic size. 



Biotite and hornblende, of usual characters, are nearly always 

 fresh, chlorite and epidote being the more frequent alteration 

 products. 



In the following table is given a chemical analysis of this rock by 

 L. G. Eakins, together with others of nearly allied intrusives of other 

 localities. The corresponding norms are shown in another table. 

 Both anatyses and norms have been taken from Washington's Tables.^ 

 All analyses were made in the laboratory of the United States Geo- 

 logical Survey. 



Table of analyses 



^ Washington, H. S., Chemical Aaalyses of Igneous Rocks, U. S. Geol. Suive.y Prof. 

 Paper 99, 1917. 



