1. Foliated metamorphic rocks: These rocks have a layered or banded appearance due to the alignment of mineral grains under pressure. Examples include slate, schist, and gneiss.
2. Non-foliated metamorphic rocks: These rocks lack a layered appearance because their minerals are randomly oriented. Examples include marble, quartzite, and hornfels.
3. Contact metamorphic rocks: These rocks are formed when existing rocks are altered by the heat and pressure of an igneous intrusion. They can be either foliated or non-foliated, depending on the specific conditions of their formation.
So, while it's common to talk about foliated and non-foliated metamorphic rocks, remember that contact metamorphic rocks are a distinct category within the broader classification.
