222 WATSON AND CLINE ROCKS OF THE BLUE RIDGE REGION 



Analysis of Unakite, Milams Gap, Virginia 



(W. O. Phalen, analyst) 



Per cent 



Si0 2 58.32 



A1 2 3 15. 77 34 



Fe 2 3 6.56 



FeO 89 



MgO 09 



OaO 11.68 



Na 2 32 



K 2 4.01 



H 2 1.73 



P 2 5 48 



MnO >. 13 



ZrO, trace 



99.98 

 ORIGIN OF THE UN A KITE 



The unakite-bearing rock of the Unaka Mountains of western North 

 Carolina and eastern Tennessee is a coarse biotite granite varying from 

 porphyritic to even-granular in texture, usually exhibiting pronounced 

 secondary gneissoid structure, and mapped by Keith 35 as the Max Patch 

 granite of Precambrian age. In the Blue Eidge of Virginia the unakite- 

 bearing rock, where observed, is a quartz-bearing hypersthene-andesine 

 syenite, previously described by Phalen 36 in the Milams Gap locality as 

 hypersthene akerite. In each instance it seems entirely clear that the 

 unakite and its associated rock are derived from the same magma, and all 

 who have studied the unakite from the several localities are in agreement 

 that epidote, one of the essential minerals, is secondary in origin; also 

 that the epidote has developed from feldspar and the mafic constituents 

 (biotite in the North Carolina-Tennessee area, and pyroxene and to some 

 extent hornblende in the Virginia area) through chiefly hydrometamor- 

 phism (action of percolating meteoric waters) , aided probably by dynamic 

 metamorphism. 



Only certain very restricted parts of the rock of either State are 

 unakite-bearing. From the senior writer's studies of the Madison County, 

 North Carolina, area it seemed quite conclusive, from the different ex- 

 posures studied of the unakite in its relations to the epidote-bearing 

 granite, that it was of distinct vein character, which can be referred very 

 likely to the segregation type. It is suggested, then, that in some cases 



M Includes Ti0 2 . 



35 Arthur Keith: Asheville Folio (No. 110), Geol, Atlas U. S., U. S. Geol. Survey, 1904. 



89 W. C. Phalen : Op. cit. 



