Study Geography notes on Weathering and Rocks for Secondary. Useful for revision, homework, and exam preparation in Zimbabwe.
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Weathering of Rocks FORMATION OF ROCKS Rock can be classified into three groups based on their formation or origin. 1. IGNEOUS ROCKS These rocks are directly formed from the cooling or solidification of molten rock or magma. Types of Igneous rocks a) Extrusive or Volcanic rocks - these are formed by the solidification of molten material that has come out of the interior of the earth onto the surface of the earth. An example is basalt. b) Intrusive or Plutonic rocks - these are formed when magma cools more slowly underground often at very great depths. They are different from volcanic rocks because they have larger crystals because of their slower rate of cooling. Examples include granite and Dolorite. Granite covers large areas of Zimbabwe and forms beautiful landforms on the landscape when later exposed e.g. Ruwares in Domboshawa, Castle kopjes in Matopo, Balancing rocks in Epworth. Economic Uses of Igneous rocks Igneous rocks usually withstand the effects of weathering very well and are therefore use for building memorials, roads, bridges and buildings. 2. SEDIMENTARY ROCKS - These are formed from the accumulation of rock particles or sediments derived from other rocks and are therefore called Derived rocks. - The materials have been deposited in layers or strata by agents such as water, wind and ice and the layers are cemented together due to pressure. Characteristics of Sedimentary rocks 1. They are stratified or layered. 2. All sedimentary rocks are non crystalline(not formed of crystals) 3. Some sedimentary rocks contain fossils Economic value of sedimentary rocks 1. Coal - this is used as a fuel both in homes and industry and it has by products which are used in the chemical industry. 2. Limestone - it is used as a flux in the processing of iron ore 3. Clay - this is used in the manufacture of cement, bricks and china (cups, plates e.t.c) 3. MERTAMOPHIC ROCKS - These are either igneous or sedimentary rocks which have become changed when subjected to great heat and pressure. - Under such forces, the rocks are mertamophosised into other rocks of another type. 1 Print to PDF without this message by purchasing novaPDF (http://www.novapdf.com/)