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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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