5Igneous Rocks Igneous comes from the Latin word ignis, meaning ‘fire’. Igneous rocks are formed when molten material from within the Earth cools and becomes solid.Molten material is called magma when it is below the Earth’s surface, and lava when it is above the Earth’s surface.Magma reaches the Earth’s surface when volcanoes erupt.
6Intrusive Igneous Rock When magma cools slowly below the Earth’s surface it forms intrusive rocks.Granite is an example of a slow-cooling igneous rock in which crystals can be seen with the naked eye.
7Extrusive Igneous Rock Lava cools more quickly than underground magma because it is above the Earth’s surface.Cooling lava forms extrusive rock.Crystals formed are small or non-existent. Basalt is an example of an extrusive igneous rock containing tiny crystals.
9What are igneous rocks used for? Igneous rocks are extremely hard and are useful building materials.Bluestone is one example, used in Melbourne for constructing buildings, gutters and laneways.
10What are igneous rocks used for? Ancient tools made from igneous rocks have been found in Australia.Indigenous Australians used greenstone to make axes
11Sedimentary RocksName comes from Latin words sedimentum, meaning ‘settling’, and sedere, meaning ‘to sit down’.Made from sediment which is small, broken-down bits of other rocks and the remains of animals and plants.Sediment is compressed and stuck together in a process known as lithification.
12Lithification Step 1: Sediment builds up to form a layer. Pressure from the material above squeezes out any air or gaps.The particles interlock.Step 2:Water seeps through the sediment carrying with it minerals that cement the particles together even more strongly.
15Uses of Sedimentary Rocks Easy to splitSandstone used in building and paving materialsLimestone can be ground up to make cementCoal is burnt to produce electricity
16Metamorphic Rocks Metamorphic means ‘to change form’ Rocks may be changed by heat and pressure within the EarthA rock made this way is stronger than the original material because its particles are fused together.
17Metamorphic RocksSlate and Marble are two examples of metamorphic rocks.