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Cumulative work over the last twenty years has defined the glass-forming regions in several M–Si–Al–O–N systems (M=Mg, Ca, Y, Ln) with the resulting crystalline products identified after heat treatment. Glass-forming regions in nitrogen-rich sialon glasses have been recently reported and heat treatment of some of these glasses in the Y–Si–Al–O–N system has been performed. The crystallization of yttrium-containing glasses is particularly sensitive to small variations in composition and heat treatment temperature and in the current work the results of three series are discussed: (1) a single composition, Y15.2Si14.6Al8.7O54.6N6.9 (16 e/oN), treated at 30 °C intervals between 875–1410 °C; (2) compositions of a constant Y: Si:Al ratio of 3:3:2 and up to 32 e/oN and (3) selected compositions lying on the 28 e/o N plane. Two different sets of crystalline products are found to form above and below 1200 °C.