Two major mineralogic types of mafic enclaves (amphibolite and pyroxene-amphibolite) have been characterized in the Morton quartzofeldspathic gneiss at Morton, Minnesota. Some amphibolite contains plagioclase megacrysts with An₆₆ cores and An₄₃ rims. One indication of compositional equilibration of the amphibolite with host gneiss is the presence of biotite-rich rims on many enclaves. Textural and compositional reaction relationships observed in the mafic enclaves may be interpreted as relict igneous features. Bulk compositional data from three representative enclaves at Morton suggest that the pyroxene amphibolite could be derived from amphibolite by crystal fractionation and that both enclave types could have crystallized from a tholeiitic magma.