Here's a breakdown:
Texture:
* Foliated: Rocks with a layered or banded appearance due to the alignment of minerals during metamorphism. Examples:
* Slate: Fine-grained, with a slaty cleavage (splits easily into flat sheets).
* Phyllite: Slightly coarser than slate, with a silky sheen.
* Schist: Medium- to coarse-grained, with visible mineral crystals.
* Gneiss: Alternating bands of light and dark minerals.
* Non-foliated: Rocks that lack a layered appearance due to the absence of directed pressure during metamorphism. Examples:
* Marble: Metamorphosed limestone, often recrystallized calcite.
* Quartzite: Metamorphosed sandstone, primarily composed of quartz.
* Hornfels: Fine-grained, often formed by contact metamorphism.
* Anthracite: Metamorphosed coal, with a high carbon content.
Mineral Composition:
* Specific minerals: Rocks are further classified based on the dominant minerals present. For example, a schist dominated by mica would be classified as a mica schist.
* Chemical composition: The chemical composition of the parent rock also influences the resulting metamorphic rock. For example, limestone (calcium carbonate) will metamorphose into marble, while sandstone (primarily quartz) will metamorphose into quartzite.
Beyond Texture and Composition:
While texture and composition are the main criteria, there are other factors that can help classify metamorphic rocks, including:
* Grade of metamorphism: The intensity of heat and pressure experienced during metamorphism.
* Type of metamorphism: Contact metamorphism (heat from igneous intrusions), regional metamorphism (pressure from tectonic forces), or dynamic metamorphism (along fault zones).
Important Note: There's significant overlap between different rock classifications, and some rocks might fit multiple categories depending on the criteria used.
Let me know if you want more details about specific rock types or any of the classification factors!
