1. Texture:
* Original Texture: Igneous rocks often have a crystalline texture, while sedimentary rocks are characterized by layers and grain sizes.
* Metamorphic Texture: Metamorphism leads to a re-crystallization of minerals, resulting in new textures like:
* Foliation: A layered or banded appearance due to the alignment of minerals under pressure (e.g., schist, gneiss).
* Non-foliated: A granular or massive texture where minerals are randomly arranged (e.g., marble, quartzite).
2. Mineral Composition:
* Original Composition: Minerals in igneous and sedimentary rocks depend on their origin.
* Metamorphic Composition: Metamorphism can change the existing minerals or create entirely new ones through:
* Recrystallization: Existing minerals are re-arranged and may change their size and shape.
* Neocrystallization: New minerals form due to chemical reactions triggered by heat and pressure.
3. Density and Hardness:
* Original Density and Hardness: Vary widely depending on the original rock type.
* Metamorphic Density and Hardness: Metamorphism often increases density and hardness. Recrystallization and the formation of denser minerals contribute to this.
4. Color:
* Original Color: Dependent on the minerals present in the original rock.
* Metamorphic Color: Color can change dramatically due to the formation of new minerals. For example, limestone (white) becomes marble (often white, but can be colorful due to impurities).
5. Other Properties:
* Porosity: Metamorphism often reduces porosity, as minerals become more tightly packed.
* Permeability: Similarly, permeability can decrease due to the reduction in pore spaces.
* Chemical Composition: Metamorphism may alter the chemical composition of the rock by introducing or removing elements.
In essence, metamorphism is a process of transformation that significantly alters the texture, mineral composition, density, hardness, and other properties of a rock. This transformation is driven by the immense heat and pressure found deep within the Earth's crust.
