Metamorphic describes a change in rock type. Specifically, metamorphic rocks are rocks that have been transformed from their original state – whether that was an igneous, sedimentary, or even an earlier metamorphic form. This transformation happens through intense geological forces.
How Do Rocks Become Metamorphic?
Metamorphism isn't just a minor alteration; it's a substantial change. The primary drivers of this change include:
- High Heat: Elevated temperatures can cause the minerals in a rock to recrystallize, changing its texture and composition.
- High Pressure: Extreme pressure, often caused by the weight of overlying rocks or tectonic forces, can compress and deform rocks.
- Hot, Mineral-Rich Fluids: These fluids can circulate through rocks, facilitating chemical reactions and altering the minerals present.
- Combination of Factors: In most cases, metamorphic rocks are formed due to a combination of two or all three of these forces.
Types of Metamorphic Changes
The changes that occur during metamorphism can result in:
- Recrystallization: Existing minerals reform into new, more stable minerals.
- Changes in Texture: The arrangement of grains within the rock can change, creating new patterns.
- Changes in Mineral Composition: New minerals can form, or some existing minerals can break down, as a result of chemical reactions.
Examples of Metamorphic Rocks
Here are some examples of metamorphic rocks and their parent rocks:
| Metamorphic Rock | Parent Rock | Metamorphic Process |
|---|---|---|
| Marble | Limestone | Heat and pressure |
| Slate | Shale | Low-grade metamorphism due to heat and pressure |
| Quartzite | Sandstone | High temperature and pressure |
| Gneiss | Granite, shale, etc. | High-grade metamorphism, involving heat and pressure |
In summary, a metamorphic rock is not born as such; it’s created when other rocks are transformed by intense heat, pressure, and/or mineral-rich fluids, causing significant changes in their original form.
