Metamorphic rock Sunday, 17 February 2019 Learning objectives: To learn the physical properties of metamorphic rocks and the processes involved in their formation.

Metamorphic rock Display this statement on the board: ‘Metamorphosis: Heat and pressure changes layers deep in the Earth’. Ask students to make a model of a sedimentary rock using two different colours of modelling clay. Underline the word ‘pressure’ and ask students to squeeze the modelling-clay rock as hard as they can and then write down the shape and appearance of the new rock. Explain that students have carried out a process called ‘metamorphosis’ on their modelling-clay rocks. Ask students to consider the conditions they created in order to make the modelling clay change (i.e. heat: warming the modelling clay in their hands; pressure: squashing the modelling clay).

Limestone or marble? Bath Abbey, England

Limestone or marble? The Taj Mahal, India

Conditions are hostile beneath your feet… Metamorphic rocks Conditions are hostile beneath your feet… Just 15 km below the Earth’s surface the temperature is a scorching 400°C. The pressure at that depth is 4000 times greater than the surface pressure.

Heat makes rocks change Metamorphic rocks Heat makes rocks change In some places, hot magma comes close to the surface. It heats up the rocks around it. Heat makes rocks change.

Metamorphic Rock Metamorphic Rock

Metamorphic rocks Making marble When limestone gets hot, its atoms rearrange themselves in a new pattern. This makes big crystals which interlock tightly. A new rock has formed. Its name is marble. There has not been a chemical change. Limestone under high temperatures and pressures can be turned into marble.

Metamorphic rocks Making slate Mudstone is a mixture of minerals. When new mountains form, high underground pressures squash mudstone. Water is squeezed out of the mudstone. There are chemical reactions between the different minerals in the mudstone. New crystals form and arrange themselves in layers. This is a new rock – slate. Mudstone under high temperatures and pressure turns into slate.

Metamorphic rocks Metamorphic rocks Marble and slate are metamorphic rocks. Metamorphic rocks form when heat, high pressure, or both, change igneous or sedimentary rocks. The rocks remain solid during the process. They do not get hot enough to melt.

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