UNAKITE TYPE 221 



restricted in distribution to the localities published, as the writers have 

 noted its occurrence in many places in the Blue Eidge of Virginia in 

 association with the type (hypersthene-orthoclase-bearing quartz diorite) 

 described above. In the many occurrences noted the rock shows consider- 

 able variation, both in color and in composition. Usually two phases are 

 recognized: (1) A highly feldspathic phase in which pink or red feld- 

 spar amounts to three-fourths of the mass, the other two essential con- 

 stituents being yellow green epidote and white to smoky quartz; and (2) 

 a non-feldspathic phase composed of quartz and epidote and designated 

 epidosite. Feldspar is not apparent in hand specimens of the epidosite 

 phase of the rock, but is recognized microscopically in some thin sections. 

 Other variations are into essentially all quartz on the one hand and into 

 essentially all epidote on the other. All gradations between the two prin- 

 cipal phases of the rock mentioned above are noted. 



The rock is low in quartz, but contains much epidote. The feldspar is 

 usualty orthoclase or microcline, or both. Plagioclase is rare in the thin 

 sections studied, and mafic minerals have not been identified. From its 

 mode of occurrence and association in the thin sections studied, epidote is 

 clearly a secondary mineral. Its microscopic description by the senior 

 writer in the unakite of Madison County, North Carolina, is essentially 

 similar to that of the Blue Eidge, Virginia, occurrences and is quoted in 

 full. 33 



"It [epidote] occurs in large masses composed of minute microscopic gran- 

 ules, many of them replacing the entire feldspar individuals, and as continu- 

 ous and irregular disconnected bands and areas of large and small size, fol- 

 lowing the fractures in both the feldspar and the quartz, but most extensively 

 developed in the feldspar. The development of epidote along the breakage 

 lines can be continuously traced in many places from the larger areas or 

 masses replacing the entire feldspar individuals across or into contiguous feld- 

 spars. In still other places the feldspar shows scattered granules of epidote 

 over its surface. All gradations between these two extremes of epidotization 

 appear. Hardly any of the feldspar in the sections examined was entirely 

 free from some epidotization." 



The commonest accessory minerals are zircon, apatite, and iron oxide. 

 A chemical analysis of the unakite from Milams Gap, in the northern 

 Blue Eidge of Virginia, gave the following result : 



33 Thomas L. Watson : Bull. 426, IT. S. Geol. Survey, 1910, pp. 158-159 ; see also Jour. 

 Geol., vol. xii, 1904, p. 397. 



