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How are rocks formed?

How are rocks formed?

In this enquiry we will be finding out all about how different types of rocks are formed and how they can be identified. Use the links and information on this page to find out more about rocks.






Facts about Rocks

  • Rocks and stones are naturally occurring solids made up of minerals.

  • The Earth’s crust is made up of rock.

  • Rocks have been used by humans for millions of years, from early tools and weapons through to various construction materials.

  • There are three different types of rocks based on the way they form, igneous, sedimentary and metamorphic.

  • When magma cools and solidifies it forms igneous rock.

  • Examples of igneous rocks include granite, basalt, gabbro, obsidian and pumice. More igneous rock facts.

  • Sediment deposited over time, often as layers at the bottom of lakes and oceans, forms sedimentary rocks.

  • Examples of sedimentary rocks include sandstone, mudstone, flint, greywacke and chalk. More sedimentary rock facts.

  • Extreme pressure and heat over time forms metamorphic rocks.

  • Examples of metamorphic rocks include marble, quartzite, schist, granulite and slate. More metamorphic rock facts.

  • The metamorphic rock marble is formed from the sedimentary rock limestone.

  • The metamorphic rock granulite is formed from the igneous rock basalt.

(Taken from

What are the different types of rocks?

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The three main types, or classes, of rock are sedimentary, metamorphic, and igneous and the differences among them have to do with how they are formed.

Sedimentary rocks are formed from particles of sand, shells, pebbles, and other fragments of material. Together, all these particles are called sediment. Gradually, the sediment accumulates in layers and over a long period of time hardens into rock. Generally, sedimentary rock is fairly soft and may break apart or crumble easily. You can often see sand, pebbles, or stones in the rock, and it is usually the only type that contains fossils.

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Examples of this rock type include conglomerate and limestone.

Metamorphic rocks are formed under the surface of the earth from the metamorphosis (change) that occurs due to intense heat and pressure (squeezing). The rocks that result from these processes often have ribbonlike layers and may have shiny crystals, formed by minerals growing slowly over time, on their surface.

Examples of this rock type include gneiss and marble.

Igneous rocks are formed when magma (molten rock deep within the earth) cools and hardens. Sometimes the magma cools inside the earth, and other times it erupts onto the surface from volcanoes (in this case, it is called lava). When lava cools very quickly, no crystals form and the rock looks shiny and glasslike. Sometimes gas bubbles are trapped in the rock during the cooling process, leaving tiny holes and spaces in the rock.

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Examples of this rock type include basalt and obsidian.
(The above is taken from


Click the pictures below to do some more research!

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1 Comment

  1. Anonymous

    I really enjoyed doing my home work, it was fun making my big rock poster with my mummy.

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