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Polymorphism identification and geology

The phenomenon in which a single chemical compound can crystallize in two or more different crystal structures, each representing a distinct mineral species. The different polymorphs are stable under different temperature-pressure conditions, and transformations between them can be used as geothermometers or geobarometers. Polymorphism is distinct from isomorphism, which involves different compositions with the same structure. Field: mineralogy. Example: The Al₂SiO₅ polymorphs—andalusite, kyanite, and sillimanite—are stable under different pressure-temperature conditions, and their occurrence in metamorphic rocks is a direct indicator of the P-T conditions during metamorphism.. Related terms: Isomorphism, Crystal structure, Phase diagram, Allotropy.

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  • Isomorphism

Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner
GeoMiner
Last updated
2026-03-30T15:19:42.127987+00:00
Review status
Published; not independently peer-reviewed
  • USGS Thesaurus — U.S. Geological Survey. Controlled earth-science terminology used to describe USGS information resources.
  • Glossary of Geologic Terms — U.S. National Park Service. Geologic definitions prepared by the NPS Geologic Resources Inventory.

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Common questions

What does Polymorphism mean in geology?
The phenomenon in which a single chemical compound can crystallize in two or more different crystal structures, each representing a distinct mineral species. The different polymorphs are stable under different temperature-pressure conditions, and transformations between them can be used as geothermometers or geobarometers. Polymorphism is distinct from isomorphism, which involves different compositions with the same structure.
What is an example of Polymorphism?
The Al₂SiO₅ polymorphs—andalusite, kyanite, and sillimanite—are stable under different pressure-temperature conditions, and their occurrence in metamorphic rocks is a direct indicator of the P-T conditions during metamorphism.
Which earth-science field uses the term Polymorphism?
Polymorphism is used in mineralogy.
Which terms are related to Polymorphism?
Related terms in this reference are Isomorphism, Crystal structure, Phase diagram, Allotropy.

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