Cristobalite Alpha/Beta Displacive Transformation

The movie clip to the left shows a multiple solid inclusion, 30 micrometers in length, enclosed in garnet from the Barton Mine, south-central Adirondack Mtns, NY, USA. The inclusion contains two crystals of alpha-cristobalite (with fractures), two opaque crystals of ilmenite, and the mineral filling the remaining space is albite. The clip shows alpha-cristobalite going through its displacive transformation to beta-cristobalite. The clip starts at 260 C and ends at 270 C. The transformation is characterized by a 5 % volume increase and manifests itself by the sequential closing of fractures. For more information, see: Darling, R.S., Chou, I-M., and Bodnar, R.J., 1997, An occurrence of metastable cristobalite in high pressure garnet granulite: Science, v. 276, p. 91-93.

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Page Created: Sept, 1998; Last modified: Aug, 2007