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8.2 Igneous rocks Igneous rocks are formed from magma. © Oxford University Press 2009 8.2 Igneous rocks Big crystals or small? Magma cools more quickly on the surface to make rocks with smaller crystals. These are extrusive igneous rocks. Magma cools slowly underground to form rocks with big crystals. These are intrusive igneous rocks. © Oxford University Press 2009 8.2 Igneous rocks Rocks are a mixture of minerals. • Minerals are elements or compounds that occur naturally in the Earth. They usually have a crystal structure. • Rocks are made up of a number of minerals. © Oxford University Press 2009 8.2 Igneous rocks Rocks are a mixture of minerals. © Oxford University Press 2009 8.2 Igneous rocks Most igneous rocks are… …hard and strong © Oxford University Press 2009 8.2 Igneous rocks …and non-porous (water doesn’t soak into them) © Oxford University Press 2009 8.2 Igneous rocks Granite is hard, strong and non-porous That’s why it makes great kerbstones… … and kitchen worktops © Oxford University Press 2009 8.2 Igneous rocks Basalt was formed when magma cooled quickly, say under the sea. So basalt has small crystals – you need a hand lens to see them. © Oxford University Press 2009
