Within the area of the Idaho batholith, remnants of schist presumably of the Belt series, contain zones of orbicular rocks. The orbicules consist mainly of radiating perthitic-like intergrowths of plagioclase. A complete sequence in the schist from groups of feldspar porphyroblasts indicates a metamorphic rather than a magmatic origin. Gradations from a schist with orbicules to a rock composed chiefly of orbicules indicate that this orbicular rock was formed by metasomatic processes.

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