1. Metamorphic Rocks
Section 3.4

2. Formation of Metamorphic Rock
Metamorphic rocks form when existing rocks are changed by heat and pressure
Metamorphism means “to change form”
Most of the changes occur at elevated temperatures and pressures. These conditions are found a few kilometers below Earth’s surface and extend into the upper mantle
Metamorphism occurs in two ways: contact and regional

3. Contact Metamorphism Changes caused by heat from nearby magma
Produces low-grade metamorphism
Marble often forms when magma intrudes limestone

4. Regional Metamorphism
During mountain building, large areas of rock are subjected to extreme pressure and temperatures
Regional metamorphism results in large-scale deformation and high-grade metamorphism

5. Agents of Metamorphism
There are three agents of metamorphism
Heat
Pressure
Hydrothermal solutions
During metamorphism, rocks are usually subjected to all three agents

6. Heat
Heat is the most important agent of metamorphism because it provides the energy needed to drive chemical reactions
The heat comes from magma and the change in temperature with depth

7. Pressure (Stress)
Pressure on rocks within Earth is applied in all directions
Pressure causes the space between the mineral grains to close, resulting in a more compact rock with a greater density
The mineral grains tend to
flatten and elongate
Pressure can cause minerals
to recrystallize into a new mineral

8. Hydrothermal Solutions
Water solutions that surround mineral grains aid in recrystallization by making it easier for ions to move
Hot, watery solution that escapes from a mass of magma during the later stages of crystallization is called hydrothermal solutions
A change in a rocks overall composition may occur

9. Classification of Metamorphic Rocks
Metamorphic rocks can be classified by texture and composition
The texture of metamorphic rocks can be
Foliated – a rock with layered or banded appearance
Nonfoliated – a rock without a banded texture

10. Foliated Metamorphic Rocks
A rock with a banded or layered appearance is called a foliated metamorphic rock
When rocks are exposed to greater temperature and pressure, the minerals will become compacted and may recrystallize with a preferred orientation

11. Nonfoliated Metamorphic Rocks
A metamorphic rock that does not have a banded texture is called a nonfoliated metamorphic rock
Most nonfoliated rocks contain only one mineral

12. Summary of Metamorphic Rocks
Most metamorphic changes occur at elevated temperature and pressure
During contact metamorphism, hot magma moves into rock
Regional metamorphism results in large-scale deformation and high-grade metamorphism
The agents of metamorphism are heat, pressure and hydrothermal solutions
Classified by texture as foliated or nonfoliated

13. Table 3 on page 84