Science Focus Topic 2 Notes: Rocks and The Rock Cycle | Print |
Rocks are classified into 3 major groups

Igneous Rock

- forms when hot magma (or lava) cools and solidifies
Magma is melted rock found below the Earth's crust
- Types of Igneous rock are:

  • intrusive (cooled and hardened magma below the Earth's surface
  • extrusive (rock that forms when lava - magma released during a volcanic eruption - cools on the surface)

- Magma can contain crystals, their size depending on how quickly or slowly the rock cools (large crystals form when the rock cools slowly)
- Investigation 5-B Forming Crystals p.362-363

Sedimentary Rock

- is formed from sediment (loose material - rock, minerals, plant and animal remains - that is layered and compacted together by the pressure of the material above it)
stratification is the visible evidence of the layers
cementation - some of the minerals that dissolve with the addition of water, makes a natural cement that glues the pieces of sediment together.
Types of sedimentary rock include:

  • shale (formed from fine clay or mud)
  • sandstone (sand, made of quartz)
  • conglomerate (pebbles and small stones cemented together)
  • limestone (organic sedimentary rock, containing fossils - plant and animal remains)

Metamorphic Rock

This type of rock has changed its form from what it was originally. It is formed below the Earth's surface by extreme pressure and heat
- the parent rock will become another type of rock depending on how much pressure and heat is used to change it
- example:
shale ---» slate ---» schist

The Rock Cycle
another visual
Rocks are constantly changing. The Rock Cycle does not have a set order as they are weathered, consolidated, buried, melted and solidified

Techniques for Identifying Rocks

- appearance
- type of mineral/s present (viewed through a microscope)

Sediment and Soil

Some sediment becomes soil
soil formation is determined by climate, type of rock present, amount of water, organic material, air spaces, living organisms in the soil.
- decaying material in the soil is called
compost, when mixed with other matter, it becomes the dark-coloured portion of the soil called humus
humus is rich in nitrogen, phosphorus, sulphur and potassium, which dissolve in water, making the soil fertile (supplying nutrients for plant growth)

Soil Profiles

Soil forms slowly over time.
It has been classified into layers, giving it a soil profile.
topsoil (dark rich soil containing humus and small grains of rock
subsoil (lighter in colour with little or no humus - contains minerals that have been leached from the topsoil) Leaching is the removal of materials in the soil that can be dissolved in water.
- the bottom layer contains partly weathered rock and minerals leached from above and closely resembles the
parent rock below it.


- Igneous derived from Latin ignis, meaning fire
- Building and road construction, pulp and paper and ornamentation uses limestone (which is easily cut and shaped) and sandstone (which is easily mined)
- Space rocks land on the surface from Meteorites - which are highly magnetic and similar to earth rocks
Granirex (made from granite) is a building material that is only 1cm thick. Find out more at
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