Rock Cycle

• how are igneous rocks formed?

  the cooling and crystallisation of molten rock / magma
• how are sedimentary rocks formed?

  the cementing and compaction of weathered / eroded sediment grains
• how are metamorphic rocks formed?

  heat and pressure affecting existing rock
• the disintegration or decomposition of insitu rock is known as

  weathering
• examples of chemical weathering would include:

  hydrolysis , carbonation etc.
• the destruction of rocks by the force of moving agents is...

  erosion
• there are several types of erosion:

  • attrition - grains colliding with each other
  • abrasion - grains colliding with another substrate
  • hydraulic action - force of water
• freeze-thaw weathering


  when water gets into cracks in rocks, freezes, and expands by 9%. this process repeats and eventually breaks the rock and causes rockfall
• plutonic and volcanic are two types of igneous rocks:


  plutonic - slow crystallisation of underground magma, composed of large crystals and silicate minerals

  volcanic - rapid crystallisation of surface lava, composed of small crystals and silicate minerals
• the energy that powers the rock cycle comes from internal and external sources
• external energy sources power surface processes (weathering, erosion, transportation)

  • solar energy - warms earth's atmosphere and causes rock weathering/erosion (e.g. insolation weathering)
  • gravity - causes rivers / glaciers to flow downhill which leads to erosion and transportation
• internal energy sources power uplift of rick, metamorphism, and melting

  • radioactive decay - decay of unstable elements (e.g. uranium)
  • heat generated by enormous pressures within the earth
  • residual heat - i.e. heat in the core left over from the early molten phase