Recrystallization:
* Original minerals in the parent rock (protolith) are rearranged and reorganized into larger crystals.
* This happens due to the increased heat and pressure during metamorphism.
* The new crystals are often more stable under the new conditions.
Changes in mineral composition:
* The original minerals in the protolith react with each other and/or with fluids circulating through the rock.
* This leads to the formation of new minerals that are stable at the metamorphic conditions.
Absence of Foliation:
* Non-foliated metamorphic rocks lack the aligned minerals and banded appearance characteristic of foliated rocks.
* This is because they experienced metamorphism under equal pressure from all sides, or limited deformation.
Examples of Non-Foliated Metamorphic Rocks:
* Marble: Formed from limestone or dolostone, characterized by its recrystallized calcite or dolomite crystals.
* Quartzite: Formed from sandstone, composed primarily of interlocking quartz crystals.
* Hornfels: Often formed by contact metamorphism, displaying fine-grained texture.
Key Takeaway:
While non-foliated metamorphic rocks do undergo changes, these changes primarily involve recrystallization and mineral composition changes, without creating a layered or banded appearance.
