Metamorphic Rocks

To get you thinking…

• Do you notice the

white bands rippling

through this cliff

face?

• How do you think this

occurred?

Metamorphic Rocks

Recognizing Metamorphic Rock

Metamorphism – the process in which one type of

rock changes into metamorphic rock because of

chemical processes or changes in temperature and

pressure

Heat &

Pressure

Limestone Marble

Metamorphic Rocks

Metamorphic Minerals

During metamorphism, heat, pressure, and hot fluids

cause some minerals to change into other minerals.

Minerals that change in this way are said to undergo

solid-state alterations.

Scientists identify the metamorphic conditions that create

specific minerals

When these minerals are found in a rock sample,

scientists are able to interpret the conditions inside the

crust during the rock’s metamorphism.

Metamorphic Rocks

Metamorphic textures

Foliated metamorphic rock – the metamorphic rock texture in which mineral grains are arranged in bands

Severe heat and pressure can cause minerals in rock to become flat or needlelike

This causes minerals to align in bands

Chemical bonds are usually weakened where these bands occur

Therefore metamorphic rock has a tendency to break along these bands.

Metamorphic Rocks

Foliated Metamorphic Rock

Metamorphic Rocks

Foliated Metamorphic Rock

Schist

Slate

Gneiss

Metamorphic Rocks

Metamorphic Rocks

Metamorphic textures

Nonfoliated metamorphic rock – the metamorphic

rock texture in which mineral grains are not arranged

in planes or bands

Nonfoliated rocks are composed of minerals that

form with blocky crystal shapes

Since nonfoliated rocks do not contain minerals that

align in bands, they are typically very strong and

durable

Metamorphic Rocks

Nonfoliated Metamorphic Rock

Marble

Quartzite

Hornfels

Metamorphic Rocks

Metamorphic Rocks

Types of Metamorphism

Regional metamorphism – occurs when changes in temperature and pressure affect large regions of Earth’s crust

This type of metamorphism usually occurs when one tectonic plate moves against another, which generates lots of heat and pressure in the rocks at the edges of the tectonic plates.

Most metamorphic rock is formed this way.

Metamorphic Rocks

Types of Metamorphism

Contact metamorphism – a local change in rock that

occurs due to contact with magma

Temperatures of rock decrease as the distance from magma increases

Metamorphic effects also decrease with distance

Contact metamorphism is limited to thin zones

Metamorphic Rocks

Metamorphic Rocks

Types of Metamorphism

Hydrothermal metamorphism – occurs when very hot

water reacts with rock and alters its chemical and

mineral composition

Typically occurs as hot fluids

migrate in and out of rock

during metamorphism

Valuable ore deposits of gold,

copper, zinc, tungsten and

lead form this way

End of Metamorphic Rocks