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Rocks are used to build houses, bridges and other stable structures. Building materials may be cut from large or small stones, or processed to make bricks. Another very important building material is concrete, which is made from cement. The cement is made from the sedimentary rock limestone. |
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Harder rocks, such as the igneous rock granite or the metamorphic rock marble, can be polished to a shiny finish and are used to make a beautiful decorative surface. |
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It is not just in construction that rocks are used. Glass and other ceramics are made from rocks, by treating them with heat and the action of other chemicals. Rocks have been used as tools and weapons since the first human being appeared on Earth over two and a half million years ago. |
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