The ∆-index of 52 specimens of cordierite from an aluminous hornfels increases from 0.23 to 0.29 inward toward a quartz monzonite pluton. The MgO/(MgO+FeO) ratio in cordierite from the assemblage, cordierite-biotite-Al silicate-muscovite-quartz-plagioclase-magnetite±ilmenite±pyrrhotite±graphite(?), does not vary significantly toward the intrusive body. The A-index is independent of slight changes in MgO/(MgO+FeO) ratio and in the Al2O3/(Al2O3+SiO2) ratio.

Beryllium content in five samples ranges from 7 to 15 ppm and varies inversely with the ∆-index. The minor variations in beryllium content may reflect the ability of various structural states of cordierite to accommodate beryllium. Local variations in the ∆-index are related in a qualitative way to variations in the thermal environment, (1) near a large dike, and (2) at one corner of the intrusive body.

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