In geology, heteromorphism refers to the occurrence of a mineral in multiple crystal forms or structures that differ from one another while retaining the same chemical composition. This phenomenon arises when a mineral can crystallize in different shapes, habits, or arrangements due to variations in environmental conditions such as temperature, pressure, or chemical environment during formation.
Heteromorphism should not be confused with polymorphism, even though both involve structural variability. In heteromorphism, the focus is on differences in external form and habit rather than internal crystal structure.
Differences Between Heteromorphism and Polymorphism
| Feature | Heteromorphism | Polymorphism |
|---|---|---|
| Basis of difference | External crystal habit and form | Internal crystal structure |
| Chemical composition | Same | Same |
| Example focus | Shapes/forms of crystal | Distinct crystal lattice types |
Example: In heteromorphism, the mineral may appear as both elongated prismatic crystals and stubby blocky crystals under different conditions, even though the underlying crystal structure remains the same.
Examples of Heteromorphism in Geology
- Quartz: Can develop both pointed hexagonal prisms and massive, drusy forms depending on growth environment.
- Olivine: May show variations in crystal habit related to cooling history of the host magma.
- Calcite: Exhibits a broad range of crystal habits — from scalenohedral to rhombohedral — due to varying conditions of growth.