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8.2 Igneous Rocks (Magma and lava (As magma rises to the crust it melts…
8.2 Igneous Rocks
Magma and lava
As magma rises to the crust it melts overlying rock, changing the rock's composition
Lava is magma at the surface, it can be as hot as 1200C when it erupts, below the surface magma can be even hotter
Magma is very hot molten (melted) rock, magma is less dense than the surrounding rock, so it rises through any fault in the Earth's crust
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Igneous rocks form at the surface of the earth and also underwater, on the ocean floor
If magma reaches the surface to become lava, when it cools very rapidly, especially if the eruption happens underwater, magma that does not reach the surface cools slowly
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When lava cools quickly is forms rock with very small crystals or no crystals at all, rock with larger crystals forms when cooling occurs more slowly
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Uses of igneous rocks
Basalt - buildings, concrete, floor tiles
Dolerite - road surfaces, concrete
Most igneous rocks are very hard and strong, these characteristics make them good for building and other stone structures that need to last a long time
Granite - buildings monuments, road surfaces, kitchen benchtops
Scoria - landscaping, filters and concrete, barbecue rocks
Pumice - cleaning dead skin off feet, emery boards, for shaping nails, some soaps that feel rough on your skin
Obsidian - scalpel blade for surgery in hospitals, ornaments and jewellery; ancient people used it for cutting, spear and arrow points, and pots and vases
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