Samples of tridymite from the Steinbach meteorite were examined by ditrerential scanning calorimetry and X-ray single-crystal diffraction from room temperature to about 650 °C at 1 atm. The results confirm the existence of three phase transitions in the temperature range 350–475 °C, and a model involving O disorder is presented. In the temperature range 25–250 °C, the sequence and temperatures of phase transitions are strongly dependent on the thermal history. Crystals annealed in the stability field of the hexagonal phase develop an orthorhombic superstructure when subsequently held at temperatures between 100 and 154 °C. This superstructure has not been reported previously for Steinbach tridymite.
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