396 THOMAS L. WATSON 



pinkish-green epidote granite of medium- coarse texture and fairly 

 schistose or fohated in structure. This is not the unakite proper, 

 but may be properly designated the epidote-bearing rock. It varies 

 from a typical granite in which quartz is present in the usual amount 

 to a nearly quartzless rock of the same color and texture. The 

 unakite proper is a coarse-textured rock composed of yellow-green 

 epidote, dull pink or red feldspar, and quartz. It is not entirely 

 uniform in color and composition, but it grades into a highly feld- 

 spathic rock of pink color on the one hand, and an epidotic rock of 

 yellowish-green color on the other, with still a third gradation observed 

 into pure quartz. 



Thin sections of the epidote-bearing granite show the principal 

 minerals, quartz, orthoclase, and microcline, in about equal propor- 

 tion, a little plagioclase, biotite, epidote, chlorite, rutile, zircon, 

 apatite, magnetite, pyrite, and kaolin. The epidote distributed 

 through the sections is wholly a secondary product derived from 

 the interaction of the biotite and feldspar. It occurs in the form of 

 minute microscopic granules thickly crowded together, in many cases 

 lying next to the biotite. The mass of granules, when forming an 

 area large enough to be visible megascopically, appears as a single 

 large epidote individual rather than as separate microscopic granules. 

 Besides epidote, the feldspars are altered to a colorless mica, and 

 in some instances the original mineral is completely obscured by the 

 alteration products. At times the feldspars are much fractured and 

 broken, the fissures of which are now filled with another mineral 

 substance. Sometimes alteration has progressed along the lines of 

 fracture in the feldspar, and patches and stringers of deep-green 

 mica line them. Thread-like filaments of rutile, broken into minute 

 segments, are crowded together in the quartz anhedra. Some periph- 

 eral shattering from pressure-metamorphism is indicated in narrow 

 zones of fine-grained mosaics of quartz and feldspar partially sur- 

 rounding these two minerals. Strained shadows and fractures are 

 common to both the larger quartz and feldspar grains. 



The principal difference microscopically between the unakite and 

 the epidote-bearing rock is that of extreme epidotization of the 

 former, further marked by the absence, in those sections studied, of 

 both plagioclase and ferromagnesian minerals, identified as such. 



