Earth Science

Materials of Earth’s Crust

Metamorphic Rocks

Study Tip
Think of foliated rocks as something that is foiled. Adding foil creates a layer, so foliated rocks are layered rocks.

Metamorphism

There are two main types of metamorphism:

  • Regional metamorphism: This is caused by geological processes that affect a wide area. This process affects many sedimentary rocks because they’re already in layers. For example, limestone in mountains or other formations turns into marble as pressure from tectonic plates push the layers together.
  • Contact metamorphism: This is caused by the heat of magma covering the rock(s). Most of the rocks formed by this process are called hornfels. For example, sandstone becomes quartzite and shale becomes a hornfels containing a variety of minerals.















An example of contact metamorphism,
where magma changes the type of rock over time

Textures

There are two types of textures on metamorphic rocks:

  • Foliated: These rocks typically have layers as they’re usually formed by pressure exerted from one direction. They give off a “platy” look.
  • Non-foliated: These rocks don’t have layers, and they are described as “massive” due to their non-uniform look.
Study Tip
Think of foliated rocks as something that is foiled. Adding foil creates a layer, so foliated rocks are layered rocks.
Study Tip
The same way a person may cast a shadow over another person when they stand under the sun, planets or celestial bodies that have aligned themselves cast shadows over one another as well.
metamorphism
An example of contact metamorphism, where magma changes the type of rock over time
Picture
Rock Name
Type of Metamorpic Rock
Comments
Slate
Slate
Foliated
Metamorphism of shale
Phyllite
Phyllite
Foliated
Metamorphism of slate, but under greater heat and pressure thane slate
Schist
Schist
Foliated
Often derived from metamorphism of claystone or shale; metamorphosed under more heat and pressure than phyllite
Geniss
Geniss
Foliated
Metamorphism of various different rocks. Under extreme conditions of heat and pressure
Hornfels
Hornfels
Non-foliated
Contact metamorphism of various different rock types
Quartzite
Quartzite
Non-foliated
Metamorphism of quartz sandstone
Marble
Marble
Non-foliated
Meramorphism of limestone
Metaconglomerate
Metaconglomerate
Non-foliated
Metamorphism of conglomerate
Concept Check
  • What are the two types of metamorphism?
  • What are the two textures of metamorphic rocks?