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GEOLOGY (STRUCTURE OF THE EARTH- (CRUST- varies in thickness from about…

- - - - PHYSICAL WEATHERING- can happen because of the action of:
        
        TEMPERATURE CHANGE- solids expand when they are heated and contract when they are cooled. If the temperature changes to quickly it will cause the rock to crack and wear away.
        
        WATER AND ICE- if water enters a crack in a rock and then freezes it can cause the rock to crack.
        
        CRYSTALLISATION OF SALTS- water in the soil often contains dissolved chemicals that are left when the water evaporates.
        
        WIND- fine rock particles get carried by wind and blast against other rock surfaces, wearing the rock away.
      - CHEMICAL WEATHERING- water dissolving chemicals from soil and air will react with rock, changing or breaking it down.
      - BIOLOGICAL WEATHERING- living things and their products can break down rock.
  - - - USES OF IGNEOUS ROCKS
      - CLASSIFICATION
        
        EXTRUSIVE- large crystals don't have a chance to grow because the magma cools really fast. Two examples of extrusive igneous rocks are basalt and obsidian.
        
        INTRUSIVE- the crystals interlock with each other and they are the result of magma cooling slowly so large crystals have a chance to form. Two examples of intrusive igneous rocks are granite and dolerite.
      - FORMATION- igneous rocks are formed by magma cooling either slowly or quickly to form either intrusive or extrusive igneous rocks.
    - - CLASSIFICATION
        
        CHEMICAL- formed when minerals dissolved in groundwater crystallise within the sediments or when water evaporates, leaving behind crystals.
        
        BIOGENIC- form when dead plant matter or animal remains build up and are then cemented together.
        
        CLASTIC- are formed when sediments are laid down by wind, water, gravity and ice and the compacted and cemented together.
      - THE FORMATION OF SEDIMENTARY ROCKS- made from sediments (pieces of other rocks) the sediments form together and are compacted and cemented together.
      - GEOLOGICAL HISTORY- sedimentary rocks from layers known as strata. Sediment is originally laid down horizontally and then more and more layers form on top of that one.
      - FOSSILS- fossils are the preserved evidence of organisms that once existed on earth.
    - - TYPES OF METAMORPHIC ROCKS
        
        DYNAMIC- where the rock is altered just or mostly by heat
        
        CONTACT- where the rock is altered just is mostly by pressure.
        
        REGIONAL- where the rock is altered by heat and pressure.
      - THE FORMATION OF METAMORPHIC ROCK- this rock is formed by intense heat and/or pressure under the surface of the earth.
- - - - OPEN CUT- usually used when the mineral deposit is near the surface and where there are large quantities spread over a large area.
      - DREDGING- this method is usually used when the minerals are found in sand and a large lake can be dug and filled with water.
      - LEACH MINING- with this method, a fluid that will dissolve the mineral is injected through drill holes into the deposit and then pumped out through the recovery pipes.
      - UNDERGROUND MINING- this method is usually used when the mineral deposit is deeper and or concentrated into pockets or narrow veins