The phase transformations of natural and synthetic oxide mixtures of talc-kaolinite compositions were examined by continuous x-ray diffraction while heated to 1450° C. Diffraction intensity data show the enhanced development of protoenstatite within the sheet structure of talc, thus indicating that the growth of this mineral on firing is largely controlled by the structure of the talc. The formation temperature of cordierite, which was used as a measure of the reactivity of various starting materials, indicates that alumina in the form of mullite, rather than as corundum, is most effective in lowering the development temperature of this mineral. Additional cordierite formation, through recrystallization on cooling indicates the presence of an intermediate liquid phase in the formation of this mineral.

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