Abstract

The structure of the Webster-Addie ultramafic ring in Jackson County, North Carolina, is discussed briefly. The ultramafic ring is almost everywhere concordant with the enclosing and enclosed gneiss and is thought to have been intruded as a sheet-like mass and subsequently deformed.

The mineralogy of the dunite, websterite, and enstatite pyroxenite is discussed. A table is presented showing that the Fe2SiO4 content of nine olivines from the ultramafic ring varies only 1¼% and shows no “trend” across three quarters of the thickness of the mass. Chemical analyses are given for the two types of enstatite from the enstatite pyroxenite, and for two chromite samples and one kammererite sample. The hydrothermal alteration of chromite to kammererite is described and photomicrographs presented to illustrate the progression of this reaction toward an ideal chromite-magnetite solid solution.

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