1. Texture:
* Foliation: This is the most characteristic feature of metamorphic rocks. It refers to the parallel alignment of minerals within the rock, creating a layered or banded appearance. This is often caused by pressure and heat. Examples include slate, schist, and gneiss.
* Non-foliated: Some metamorphic rocks lack a distinct layering, exhibiting a more granular or massive appearance. Examples include marble and quartzite.
2. Mineral Composition:
* Recrystallization: Heat and pressure cause existing minerals to change their size and shape, sometimes forming new minerals altogether. This changes the mineral composition of the rock.
* Metamorphic Minerals: Certain minerals are indicative of metamorphism, such as garnet, kyanite, and staurolite.
3. Grain Size:
* Grain Size and Shape: Metamorphic rocks often exhibit a change in grain size and shape compared to their original rock. This is a result of the recrystallization process.
4. Evidence of Deformation:
* Folding: Metamorphic rocks often exhibit folds and bends, indicating that they were subjected to significant pressure and deformation.
* Faulting: Metamorphic rocks may show evidence of faulting, where rocks have broken and shifted.
5. Relationship to Parent Rock:
* Protolith: The original rock (igneous, sedimentary, or even another metamorphic rock) from which a metamorphic rock formed. Studying the protolith and the metamorphic changes can help identify the rock.
Here's how these properties can be used to distinguish metamorphic rocks from other types:
* From Igneous Rocks: Igneous rocks generally lack the foliation and metamorphic mineral assemblages characteristic of metamorphic rocks.
* From Sedimentary Rocks: While sedimentary rocks may have layers, these layers are often due to deposition rather than the pressure-induced alignment of minerals found in metamorphic rocks. Sedimentary rocks also often contain fossils, which are rarely found in metamorphic rocks.
Important Note:
It's essential to consider all of these properties together when identifying a metamorphic rock. A single characteristic might not be enough to make a definitive determination.
