A mineral layer that surrounds a mineral of different composition. The term is most often applied to minerals coating garnets, the kelyphitic rim containing orthopyroxene, spinel, clinopyroxene, and amphibole, often as two concentric layers, the outer one poor in spinel and the inner one rich in spinel. Several explanations have been proposed for the formation of kelyphitic rims; the most widely accepted is that they result from exsolution from orthopyroxene and metamorphic reaction between olivine and garnet during retrograde metamorphism.