Alpha-cristoballite

But in practice, the kinetic of the above reaction is too slow, and tridymite never forms below 1250°C, and hence at 1250°C or 1050°C in the presence of impurities, a-quartz transforms irreversibly into alpha-cristoballite (a-cristoballite, tetragonal) [14464-46-1] with an important volume change (17.4 vol.%) as follows ... 

However, if the temperature is raised to 1470°C, a-tridymite transforms also irreversibly into alpha-cristoballite (a-cristoballite) without any change in volume as follows ... 

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See also in sourсe #XX -- [ ]

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