Fassaitic diopside containing 22–23 wt% Al₂O₃ (approximately 41–43% calcium Tschermak's molecule, CaAl₂SiO₆) and melilite containing 69–43% gehlenite crystallized from a blast-furnace slag at atmospheric pressure between about 1450°C and 1250°C. The occurrence is of petrological interest because the association of pyroxene with gehlenite-rich melilite has not been recorded from experimental studies in the system CaO-MgO-Al₂O₃-SiO₂, and because of the similarity of the compositions of both minerals to pyroxene and melilite in the Ca-Al-rich inclusions of the Allende meteorite.