Garnet was selected as a suitable mineral to use in a study of nucleation based on the relationship between the number of crystals in a unit volume of rock and the chemical composition of the area. The rocks used were the Cleengort meta-pelites in the aureole of the Ardara pluton, northwestern Ireland. Chemical and modal analyses of eleven specimens are given. While several trends were noted between mineral and chemical relationships, the most accurate quantitative relationship was clearly that between the garnet (weight percent) and the FeO present, the latter dependent on completion of the reaction FeO + 2FeO<2) >3) --> Fe<3) O<4) . The mechanism of garnet formation is discussed.

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