Contact Action of Pegmatite on Schist
Introduction Pegmatites are normally small and usually occur in the parent igneous rock, so that cases of contact metamorphism directly attributable to pegmatites are rare. In connection with recent studies 2 of the Etta spodumene mine near Keystone, South Dakota, the writers’ attention was attracted by the pronounced contact zone which surrounds this remarkable pegmatite. Several specimens were selected as showing the various phases of the metamorphosed rock and these were analyzed and studied microscopically, with the results noted below. The writers are indebted to Dr. F. F. Grout for suggestions and criticisms, and to Dr. John W. Gruner for additional rock samples, necessary to complete the work. Geologic Setting of the Etta Mine The geology of the Etta mine has been described in some detail in the paper cited above. The pegmatite is one of a great series which radiate outward into pre-Cambrian schists from the Harney Peak granite batholith, . . .