Figure 6.22j. Crd + Bt Pseudomorph after Grt. Backscattered electron image of an aluminous gneiss thin section in which Crd + Bt partially replace Grt porphyroblasts, with Mn from the replaced Grt concentrated in the rims of the remaining Grt. Mn compositions of the Grt are consistent with reaction of Grt with a partial melt during decompression. J.T. Cheney photo.