1. Recrystallization:
* Heat provides the energy needed to break the chemical bonds within existing minerals in the rock.
* This allows the atoms to rearrange themselves into new, more stable mineral structures, leading to the formation of new minerals.
* The size and shape of these newly formed crystals can be quite different from the original minerals.
2. Mineral Growth:
* As heat increases, the atoms in existing minerals have more energy and are more likely to move around.
* This movement can lead to the growth of existing mineral grains or the formation of entirely new minerals.
* The process of mineral growth is often influenced by the presence of fluids and pressure.
3. Phase Changes:
* Heat can cause some minerals to change their crystal structure, resulting in a phase change.
* For example, the mineral calcite can transform into the mineral aragonite under the influence of heat and pressure.
4. Chemical Reactions:
* Heat can accelerate chemical reactions between minerals, leading to the formation of new minerals.
* This can involve the exchange of elements between minerals, the addition of new elements from the surrounding environment, or the removal of elements from the rock.
5. Foliation:
* Intense heat combined with pressure can cause the minerals within a rock to align themselves in parallel layers.
* This process, called foliation, gives the metamorphic rock a layered or banded appearance.
Examples:
* Marble: Formed from the metamorphism of limestone under heat and pressure, where calcite crystals recrystallize.
* Slate: Formed from the metamorphism of shale, where clay minerals recrystallize into fine-grained mica.
* Gneiss: Formed from the metamorphism of granite, where feldspar and quartz crystals align in alternating bands.
In summary, heat is a driving force in metamorphic processes, causing recrystallization, mineral growth, phase changes, chemical reactions, and the development of foliation, all of which contribute to the formation of metamorphic rocks.
