Metamorphic rocks are classified into two main types based on their texture: foliated and nonfoliated. The key difference between them lies in their appearance and the way they form.
Foliated Metamorphic Rocks
Foliated metamorphic rocks have a layered or banded appearance. This texture is a result of the alignment of mineral grains under intense pressure during the metamorphic process. The minerals in these rocks are flattened and elongated, creating a parallel alignment that gives the rock its foliated texture. Examples of foliated metamorphic rocks include slate, schist, and gneiss.
Nonfoliated Metamorphic Rocks
Nonfoliated metamorphic rocks, on the other hand, do not have a layered or banded structure. These rocks form under conditions where pressure is applied equally in all directions, preventing the alignment of mineral grains. As a result, nonfoliated rocks have a more uniform texture. Examples of nonfoliated metamorphic rocks include marble and quartzite.
Key Differences
- Texture: Foliated rocks have a layered or banded texture, while nonfoliated rocks have a uniform texture.
- Formation: Foliated rocks form under directed pressure, causing mineral alignment, whereas nonfoliated rocks form under uniform pressure, preventing mineral alignment.
- Examples: Foliated rocks include slate, schist, and gneiss; nonfoliated rocks include marble and quartzite.