ocr: biotite'schist country - - rock pégmatite tangential biotite defines shell poundanes Large, well developed orbicule about 20cm in diameter with many alternationg shells of biotite and plagioclase. the nucleus is a large black mass of coarse biotite with grains in concentric arrangem ent. The biotite grains in the shells are tangential to the surrace of the spheroidal shells. Near Shoup,Idaho.
