Metamorphic rocks are formed by the action of heat and pressure on existing sedimentary rocks over thousands of years. Movements in the Earth's crust push rocks underground, where they are compressed and heated, changing the mineral structure and texture. If the rocks survive this without melting, they are known as metamorphic rocks.

Examples

Slate is formed from mudstone or clay. The mudstone's plate-like particles are compressed until they are all in the same orientation. This allows the slate to be split into thin sheets that makes ideal roofing material.
Marble is formed from Limestone. Limestone shells break down into crystals, giving marble a very shiney texture and making it very hard. Marble is used as a decorative stone.

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