Metamorphic rocks are a combination of the other two types of rock found on Earth; these include sedimentary and igneous.

The name metamorphic comes from Greek words meaning “change of shape.” Metamorphic rocks have this name because they are always formed from another pre-existing rock.

How are metamorphic rocks formed?

Metamorphic rocks are formed when sedimentary and igneous rocks experience intense heat and pressure due to seismic activity in the Earth’s crust, which makes them change.

Because of this intense heat and pressure, metamorphic rocks rarely contain fossils as they are unlikely to survive.

How are metamorphic rocks formed?

These types of rocks experience intense heat because of how close they are to the magma and the amount of pressure from the Earth’s movements; this causes the rocks to get buried deeply or squeezed.

They don’t melt due to the heat. Instead, the minerals they contain change chemically, forming metamorphic rocks. If they did melt, that would mean that either igneous or sedimentary stones would form.

As well as this, changes to tectonic plates can also result in metamorphic rock formation, which occurs when they collide.

The Rock Cycle

Rocks constantly change in what is known as the rock cycle, a basic concept in geology that describes the transitions the three main rock types undergo through time. However, it takes millions of years for rocks to change!

The rock cycle explains how sedimentary, igneous, and metamorphic rocks, three rock types, are related and how processes change from one type to another over time.

Examples of metamorphic rocks

Examples of metamorphic rock include:

Marble – is formed from sedimentary rock, limestone.

Quartzite – is formed from the sedimentary rock sandstone.

Slate – is formed from the sedimentary rock mudstone.

Granulite – is formed from the igneous rock basalt.

Schist – is formed from the sedimentary rock, mudstone.

Characteristics of metamorphic rocks

  • They are formed when either igneous or sedimentary rocks are changed.
  • Heat or pressure will cause the elements in the original rock to react and reform.
  • They are crystalline and often have a “squashed” (foliated or banded) texture
  • Metamorphic rocks are usually highly resistant to weathering and erosion, making them very hard-wearing and popular for building materials.

Vital vocabulary

Metamorphic – a rock formed from pre-existing rock that has changed through heat and pressure.

Sedimentary – a rock formed when layers of mineral particles (sediment) are squashed together.

Igneous – a rock formed from magma either inside the Earth or on the surface.

Earth’s crust – the outermost solid shell of planet Earth.

Magma – the molten or semi-molten natural material found beneath the Earth’s surface.

Tectonic plates – massive, irregularly shaped pieces of Earth’s crust and uppermost mantle.

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