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Rocks and Soils

Rocks and Soils. Rock types. The Earth’s crust has many different types of rocks. These rocks are usually divided into 3 different types. Igneous Rocks Sedimentary Rocks Metamorphic Rocks. Igneous Rocks.

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Rocks and Soils

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  1. Rocks and Soils

  2. Rock types • The Earth’s crust has many different types of rocks. • These rocks are usually divided into 3 different types. • Igneous Rocks • Sedimentary Rocks • Metamorphic Rocks

  3. Igneous Rocks • These result from volcanic activity. They consists of crystals which formed as the volcanic rock cooled down. • E.g Granite, Basalt.

  4. Sedimentary Rocks • These have been layered down in layers. • They usually consist of small particles that have been eroded and transported. • E.g. Sandstone and shale. • They can also be formed from the remains of plants and animals. • E.g. Limestone, Chalk and Coal

  5. Metamorphic Rock • These rocks are those that have been altered either by extremes of pressure e.g. Shale is compressed into slate, or by extremes of heat. • E.g. limestone is changed into marble.

  6. Uses of rocks

  7. Rock Structure • The structure of a rock can among other things, affect its resistance to erosion and its permeability to water. Resistance – how hard or soft a rock is. Permeability – how much rock allows water to pass through it.

  8. Resistance • The harder a rock is, the more resistant it is likely to be to erosion. • Harder rocks thus usually form hills, mountains and steep cliffs. • Soft rocks are more liable to be worn away or broken up. • Valleys are formed in soft rocks. • On coasts, resistant rocks form steep cliffs and stand out as headlands, whereas the softer rocks form bays.

  9. Permeability • Rocks can be permeable or impermeable • Permeable rocks allow water to pass through • Impermeable rocks do not allow water to pass through. • Permeable rocks may be porous – meaning it has a lot of small pores. • Or contain areas of weakness, such as bedding planes, along which water flows. Horizontal bedding planes, on the other hand, separate individual layers of rock.

  10. Weathering and Mass movement • Weathering is the disintegration (breaking up) and decomposition (decay) of rocks in situ – that is in their place of origin. • Weathering, unlike erosion, does not involve the movement of material. • There are two main types of weathering • Physical weathering – rocks are broken down into smaller pieces. There is no change in the chemical composition of the rock. E.g. Freeze-thaw, exfoliation, biological weathering • Chemical weathering – rocks are decomposed due to chemical changes in the rock. Mostly found in warm, moist climates. An example is limestone solution.

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