Coesite and Stishovite: Stepwise Reversal Transformations.
Very marked differences in the metastable persistence of coesite and stishovite have been demonstrated; the former possibly persists indefinitely below 1000 degrees C at 1 atmosphere "dry," and the latter completely decomposes in minutes above 500 degrees to 600 degrees C to an amorphous or short range order phase. Quartz was grown (metastably) at temperatures well above its stability field from both coesite and stishovite, possibly by way of a short range order phase. The absence of stishovite in meteor-impact craters cannot be taken as evidence that it was not formed. If it has "reversed" in normal natural environments the product would almost certainly be a short range order phase or derivative.
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