What is metamorphism?

• Metamorphism means to change form.

• Metamorphic rocks are igneous, sedimentary, and other metamorphic rocks that have been changed in form (usually deep within the Earth).

What causes a rock to undergo a change in structure?

• Metamorphism of rocks is a result of high temperature and pressure (usually deep within the Earth). The extreme temperature and pressure conditions cause the atoms in existing minerals to rearrange (or change form).

What changes are observed in rocks due to metamorphic processes?

1. Metamorphic rocks become harder and more dense than their parent rocks.

High Grade = Most Dense

2. Original layers can become bent or distorted.

This distortion is the result of recrystalization of unmelted minerals under high temperature and pressure.

What is foliation?

• Foliation is an alignment of minerals, or the separation of minerals into flaky layers or light and dark bands.

• Thick banding indicates a high degree of metamorphism. (High degree means more change).

What are the types of foliation?• Schistose foliation- minerals have been squashed

into flakes of mica.

• Slaty foliation - rock splits into flat, thin layers

• Gneissic foliation – light and dark minerals are squashed into bands (Zebra stripes)

Find the foliation!

What’s the difference between banding and layering?

- Bands, like in metamorphic rocks, do not go all the way through or across the rock. - Layers, like in sedimentary rocks go all the way through like a layer in a cake.

Find the banding!

On what basis are metamorphic rocks classified?

* Foliated metamorphic rocks contain alignment of minerals, flaky layers or light and dark bands.

• Foliated metamorphic rocks are classified by the type of foliation they exhibit.

* Nonfoliated metamorphic rocks display no foliation (no layering or mineral alignment).

• Nonfoliated metamorphic rocks are classified by composition.

What are the two types of metamorphism?

1. Contact Metamorphism occurs when molten magma (or lava) comes in contact with other rocks and changes them. The primary agent of contact metamorphism is HEAT.

- Occurs over large areas, and is generally associated with mountain building

- Extreme pressures associated with the collisions of tectonic plates (mountain building) can lead to the metamorphism of rock material

2. Regional Metamorphism is the result of exposure to extreme HEAT and PRESSURE deep within the Earth.