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Definition of polysyngony

A type of polymorph where two or more minerals have the same composition, but different crystal classes owing to changed bond angles; e.g., alpha and beta quartz.

Also called displacive polymorphism. Displacive polymorphism describes structures that differ only slightly in their atomic positions/bond angles. Transitions between them are generally reversible, meaning that the crystal will spontaneously transition between the two structures due to changes in physical conditions such as temperature and pressure. This can occur because no strong bonds are broken or formed during the transition. The transition from alpha-quartz to beta-quartz is an example of displacive polymorphism and occurs at 573°C at ambient pressure. This is known as "quartz inversion" and is important in the production of ceramics.

Compare with: polytypy, polytropy, polymorphism


 
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