chapter 1: our rocky home

• rock is the hard material which makes up the surface of the earth
• earths rock first formed over 4.5 billion years ago
• rock is always changing
• rock is a mixture of materials
• a mineral is a natural compound with a chemical name and formula
• minerals usually exist in rocks as crystals
• there are three types of rock:

  • granite
  • sandstone
  • limestone
• granite are mainly silicon dioxide or quartz. most of the other minerals in it are feldspars
• feldspars are any of a group of minerals that contain calcium, sodium, or potassium
• sandstone is mainly quartz and feldspars, and is hard and resistant to weathering
• limestone is mainly calcite or calcium carbonate, mixed with quartz and other minerals
• chalk is a form of limestone
• there are ten common minerals, the rock-building minerals
• the most common minerals are feldspars and quartz. they make up most of the earths crust
• concrete is made of crushed rock and sand
• cement is made from linestone
• a scientist who studies rocks is called a geologist
• a layer of crushed frock or aggregrate is used in road building
• metals that come from rock are known as metal ore
• attractive minerals that are found in small quantities in rock are called gemstones
• gemstones are often used to make jewellery
• rocks can be put into three groups

  • igneous
  • sedimentary
  • metamorphic
• sedimentary rock forms when particles or minerals which were eroded from rock in one place gets stuck together in another place to form new rock
• a sediment of mud would give mudstone
• a sediment of sand gives sandstone
• a sediment of shells and coral gives limestone
• igneous rock forms when rock melts below ground and cools then hardens again
• metamorphic rock is rock that is changed underground without melting
• underground, heat and pressure can be enormous. together it can change the shape of a rock without melting it. the structure of the minerals usually changes, causing the rock to look different. heat and pressure cause it to metamorphose to slate, where the crystals are lined up in flat sheets.
• slate is used for roof tiles
• 65% of the earths crust is igneous rock
• 8% of the earths crust is sedimentary
• 27% of the earths crust is metamorphic
• most of the crust forming the continents is igneous rock, mainly granite
• most of the rock under the ocean is the igneous rock basalt
• igneous and metamorphic rocks show up at earths surface in places
• most of the surface is covered by a layer of sedimentary rock
• the rock cycle refers to how rocks move from one group to another
• rocks at earths surface is not stable. it is broken down to stones and sand and clay by weathering
• the rivers erode stones, sand and clay and transports them away