Igneous Rock Formation of © Boardworks Ltd 2015 How are rocks formed? Rocks are classified into three groups: sedimentary, metamorphic and igneous  Sedimentary rocks are made from deposited sediments They are quite soft, easy to shape and may contain fossils marble  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 of limestone granite © Boardworks Ltd 2015 Igneous rocks of © Boardworks Ltd 2015 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 of © Boardworks Ltd 2015 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 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 of © Boardworks Ltd 2015 Igneous rock examples of © Boardworks Ltd 2015 The formation of crystals of © Boardworks Ltd 2015 Want to see more? This is only a sample of one of hundreds of Boardworks Science presentations To see more of what Boardworks can offer, order a full presentation completely free: www.boardworks.co.uk/sciencepresentation of © Boardworks Ltd 2015