What Causes Metamorphic Rocks to Form?

Metamorphic rock is made deep within the earth
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The earth's surface and the area just below are composed of rocks and minerals. Far beneath them is a liquid center of the earth called the core. Tremendous pressure and heat transform what is above and below. Rocks are made and broken down and fused into different types of minerals. This transformation is called "metamorphism," and it creates metamorphic rock.

What is metamorphic rock?

Metamorphic rock is rock that has been created by the transformation of igneous rock. Igneous rocks are also called fire rocks. They are original rock made by magma that becomes trapped and cools. Elements such as oxygen, and compounds like silica, magnesium, iron, aluminum and calcium fuse igneous rock into other forms called metamorphic rock.

Chemical Fluid

At the bottom of the ocean, sometimes miles down, hydrothermal vents release chemicals from inside the earth. Hydrothermal vents are openings in the earth's crust that emit hot water with ions. Sulfide minerals are dissolved in black clouds that spew into the water. Metamorphic rock is formed when these chemicals cool in the ocean.


A phenomenon called "burial pressure" causes metamorphic rock to form. Pressure increases because of the weight of other rocks. This weight produces regional metamorphism. The pressure can crush other rock to form metamorphic rock. Metamorphic rocks of this type located on fault lines are known as "mylonites."


Deep within the earth where temperatures rise, regional metamorphism occurs. Heat emits from molten rock. It can heat rock to temperatures near melting and change the chemical composition of the rock. This is known as "contact metamorphism."

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