Boardworks igneous rock formation w8

Igneous Rock Formation... How are rocks formed? Metamorphic rocks have been changed by heat and pressure in the Earth’s crust..  Igneous rocks are formed from cooled magma from the m

Igneous Rock Formation

How are rocks formed?

 Metamorphic rocks have been

changed by heat and pressure in the Earth’s crust They are hard

 Igneous rocks are formed from

cooled magma from the mantle

of the Earth These rocks are

very hard and difficult to shape

 Sedimentary rocks are made from

deposited sediments They are quite soft,

easy to shape and may contain fossils

Rocks are classified into three groups: sedimentary,

metamorphic and igneous.

marble

limestone

granite

Igneous rocks

Types of magma

Magma that is high in iron

and low in silica tends to be

quite runny When a volcano

erupts, this type of magma

flows out of the volcano in a

fairly ‘safe’ eruption

Magma that is low in iron and high in silica is thick and

causes violent eruptions

Pumice, volcanic ash and volcanic bombs are produced

Igneous rock crystals

Magma is full of minerals that turn into crystals under the right conditions The size of the crystals in an igneous rock

is related to the rate at which the molten magma cools

If magma cools quickly,

the crystals do not have

very much time to form

and so are small in size

Basalt has small crystals.

On the other hand, if

magma cools slowly, the

crystals have more time to

grow and so are large

Granite has large crystals.

Igneous rock examples

The formation of crystals

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