Experiments in sealed platinum containers have been directed towards establishing the extent and stability of crystalline solutions in tridymite-M, tridymite-S and cristobalite, and lend unexpected support to the validity of the 1470° inversion in pure SiO2. Fluxes not entering into crystalline solution in either tridymite or cristobalite cause tridymite to be formed below, and cristobalite above, 1470° ± 30° C. Those forming crystalline solutions (Na+Al, Li+Al, and Ca+Al) cause a lowering of the inversion temperature. Similar experiments performed with quartz and tridymite suggest that the 870° inversion should not be hastily abandoned as a reconstructive transformation in SiO2.

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