Earth & Space - Materials from Earth - The Earth & its Resources - G15 - ES-D2.2

Learning outcomes

The three main types of rock are igneous, sedimentary and metamorphic.
Igneous rocks are formed from molten rock (magma) which has cooled.
Sedimentary rocks are formed from other rocks which have been broken down; they can contain fossils.
Metamorphic rocks are formed from other rocks which have been changed by heat and pressure.

Rock Types

The Earth’s crust is formed from three main types of rock :-

igneous - formed when magma from the mantle rises, cools and solidifies.
sedimentary - formed when materials are collected together as a result of natural processes such as erosion.
metamorphic - formed when igneous or sedimentary rock is changed by heat or pressure or both.

1. Look at a commercial collection of stones. Invite the pupils to add to the collection with any unusual samples they find. If possible visit a local beach or other source of stones.

Sort the stones into groups using a magnifying glass to help identify features on the stones. Use a rock guide to try to identify some of the samples. (See Teacher’s Notes below.)

Rocks are made up of many minerals and crystals. The children could try growing crystals.

a) Pour 200 ml of warm water into a jar and add some copper sulphate (available from your secondary school but check first with Health and Safety whether you are allowed to use it - regulations are changing all the time -be careful - it is mildly poisonous). Stir it to dissolve then add some more and stir again. Keep adding copper sulphate until no more will dissolve and crystals are left at the bottom of the solution.

b) Pour the solution into a clean jar leaving a little solution at the bottom with the undissolved crystals. Leave this to evaporate then choose one of the largest crystals and tie some thread around it.

c) Tie the thread onto a pencil and hang the large crystal in the new solution you have made. Leave it in a warm place and watch the crystal grow over the next few days.

Worksheet D4 (G) can be used to record the steps for growing a crystal.

What are Rocks?

Minerals are solid, regular mixtures of chemicals. They have characteristic features that identify them and can give them value.

Rocks are solid mixtures of minerals. They are classified by the way they were formed.

They all have distinctive characteristics.

Metamorphic and igneous rocks all consist of interlocking crystals of different minerals.

In metamorphic rocks, the crystals are often aligned in patterns, e.g. slate and schist and gneiss; in igneous rocks they are usually randomly arranged e.g. basalt and granite.

Sedimentary rocks are made of rock particles and minerals that are cemented together e.g. limestone and sandstone.

2. To mimic the effects of weathering on pumice you would need to soak the stone for a few hours and then put it in the freezer overnight. If the water has penetrated cracks in the stone then, when the water freezes, it will expand and fracture the rock.
Rock formation
Liquid magma cools and solidifies to form igneous rocks. This may happen deep underground or at the Earths surface.		Movements in the Earth’s crust bring rocks to the surface. Agents such as wind, water and ice break up the rocks into particles. Glaciers and rivers carry the particles from their original site - erosion.

Intense heat and pressure can melt rocks. When two of the Earth’s plates collide intense heat and pressure may occur, melting rocks to form new magma. Some magma returns to the surface of the Earth through volcanoes when it erupts as lava and then hardens to form new igneous rock. Magma may also be recycled in the crust when it travels up cracks and gaps then hardens to form new igneous intrusions.		The rock particles can be deposited as sediments on land, in lakes or further out to sea. Layers form as more material is deposited. The weight of successive layers compress and cement the particles together. Sedimentary rocks are formed this way. If these rocks become deeply buried they are heated by the heat from the Earth’s core and the heat and pressure form them into new metamorphic rocks.