polymorphic transformation

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polymorphic transformation Change in the atomic structure of a mineral (but not in its chemical composition) to produce a different form. In reconstructive transformation there are large energy barriers to overcome in order to break down and re-form bonds, and transition tends to be slow, e.g. graphite to diamond. In displacive transformation angles are changed between bonds, but no bonds are broken, so little energy is required, e.g. alpha to beta quartz.