Abstract

Microprobe analyses have been made of the minerals in schist samples from 14 different localities, which contain both chloritoid and staurolite. The relative Mg/Fe ratios are: garnet core < garnet rim < staurolite < chloritoid < biotite < chlorite. (Mg/Fe)Ctd/ (Mg/Fe)stl ranges from about 1.0 to 1.5, (Mn/Fe)Ctd/(Zn/Fe)Stl is near 1.0, and (Zn/Fe)Ctd/(Zn/Fe)Stl ranges from 0.5 to 0.005.

The partition data are used to construct pseudobinary T-X sections for the chloritoid-cordierite and garnet-chlorite joins of the Al2O3-K2O-FeO-MgO-SiO2-H2O system. Chloritoid + staurolite assemblages tend to contain either biotite or chlorite, indicating that the garnet-chlorite-muscovite join may break at either higher or lower metamorphic grade than the breakdown of chloritoid. Consequently, two alternative reaction sequences are possible with quartz and muscovite in excess.  
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