Earth:Dimorphism (geology)

Doubly terminated calcite crystal.

Aragonite from Spain.

Dimorphism is the property of some minerals to exist in two different crystal systems, while still having the same chemical formula. An example: CaCO₃, which exists as trigonal calcite or orthorhombic aragonite. A mineral's dimorph is the mineral that it is dimorphic with. Dimorphism is not to be confused with allotropy, which refers to a difference in crystal structure of pure elements.

Trimorphism & Polymorphism

Trimorphism is the term used when a mineral has a total of three dimorphs, while the term Polymorphism is used when there are four or more. Silica, SiO₂, is a good example, being found in nature as quartz, tridymite, cristobalite, coesite, and stishovite. Pleomorphism is a synonym of polymorphism.

See also

• Dimorphism (Wiktionary)
• Isomorphism (crystallography)
• Polymorphism (materials science)