Proterozoic fenites near Cantley, Quebec, formed from biotite gneiss and hypersthene-augite gneiss, are characterized by magnesio-arfvedsonite, magnesio-riebeckite and aegirine. In magnesio-arfvedsonite, the ratio Fe T /(Fe T +Mg) first increases and then decreases, but K remains constant with respect to Na and Ca. Magnesio-riebeckite, replacing cummingtonite or hypersthene, shows a trend similar to that of magnesio-arfvedsonite but is notably depleted in K and F. In magnesio-arfvedsonite, and possibly magnesio-riebeckite, the A sites are progressively filled. Na-amphibole and Na-pyroxene are approximately coeval. Early aegirine substitutes for the hedenbergite end-member, and later aegirine, for the diopside end-member. Late aegirine is contemporaneous with major growth of (Fe, Ti) oxides.--Modified journal abstract.

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