Metamorphic Rocks

When humans feel a lot of heat, they sweat. When a rock experiences heat and pressure, it becomes a metamorphic rock. Metamorphic rocks start as another type of rock, like an igneous or sedimentary rock, or even a different metamorphic rock. The process of creating the new rock is metamorphism —  you can think of these rocks as shapeshifters!

An image of a cliff wall made completely out of slate. Slate is a metamorphic rock.

A whole mountain of slate — a type of metamorphic rock!

How Metamorphic Rocks Form

Metamorphic rocks form through high heat and pressure deep inside the Earth or between tectonic plates. The process makes existing rocks more dense and compact. The rocks are essentially cooked and the chemicals in them rearranged so that the final rock looks a lot different than the old rock.

An illustration of the Earth's structure. Most of the inside of the Earth is magma.

Earth’s interior. Notice how there’s lots of hot magma. This can provide heat to ‘cook’ rocks.

 
There are some variations in the process, so scientists have identified names for the types of metamorphism
 

Types of Metamorphism

  1. Contact metamorphism (or thermal metamorphism) is when hot magma comes into contact with cooler rock
 
  1. Hydrothermal metamorphism occurs when hot fluids or gasses interact with rocks. 
 
  1. Shock metamorphism happens when meteorites hit the Earth’s surface (lots of pressure!). 
 
  1. Dynamic metamorphism is the creation of metamorphic rocks between tectonic plates. It happens at plate boundaries.
 
There are a few other types, but the main point is that metamorphism involves high temperatures and/or pressure to change the structure of a rock.
 

How are Metamorphic Rocks Different?

All rocks form by different minerals coming together in different ways, so it can be confusing to tell them apart. An easy rule of thumb is that igneous rocks form from fully melted rock from magma that is then cooled. Sedimentary rocks are made up of pieces of rock or animal skeletons. The pieces stick together through a process usually connected to water, like erosion.
 
Metamorphic rocks, on the other hand, are both of these types of rocks and even old metamorphic rocks that have broken up into pieces. In the Earth’s crust and upper mantle, these rocks are transformed by heat and pressure. They do not melt, because then they would be igneous rocks. Although the differences seem small, they are important to know how to identify each rock type
 

Common Examples of Metamorphic Rocks

Have you seen any of these types of metamorphic rocks in your everyday life? Read through the list to find out. 
 
  • Marble
 
  • Slate
 
  • Quartzite
 
  • Soapstone

    An image of white marble, like you might find on a countertop.

    You might find this marble rock pattern on your kitchen counter!

Other Great Resources

Simple Information About Metamorphic Rocks: http://www.onegeology.org/extra/kids/metamorphic.html

Fun Facts about Metamorphic Rocks: http://easyscienceforkids.com/all-about-metamorphic-rock/

Cool Video on Metamorphism: https://www.youtube.com/watch?v=jgK-sWkgU4o

Written by: Hayley Krolik