Rock can be hard or soft and can be porous (has space for water to get in) or non-porous (doesn’t have any spaces in it to let water in). We say that a rock is permeable if it lets water in easily, or impermeable if it doesn’t let water in at all.
Some rocks, like obsidian, are made from just one mineral. Other rocks are made from two or more minerals – for example, granite is made from feldspar, mica and quartz. Common minerals that form rocks include: feldspars, mica, quartz, calcite, dolomite, amphiboles, pyroxene and olivine.
Rocks are used for a range of purposes depending on their properties. For example, granite is very hard and impermeable, so it is often used as a building material; while chalk is a rock that wears down easily and so is used to write and draw with. Clay is used to make things like pottery and crockery because it is malleable – we can mould it.
Sedimentary rocks are formed when small particles of mineral are washed down river and are crushed and squashed at the bottom of a lake or sea while more ‘sediment’ is washed on top. This happens over millions of years. These rocks build up in layers and often have the remains of living creatures and plants fossilised within them. Examples of sedimentary rocks include sandstone, chalk, limestone and shale. Sedimentary rocks are porous and can easily be weathered or worn down.
Igneous rocks are formed from magma which is a hot, liquid found inside the earth. This either cools and forms rocks under the earth’s surface, or flows out of erupting volcanoes as lava and may mix with other minerals. It cools it forms new rocks. Igneous rocks include granite, pumice and obsidian (often called nature’s glass). Some igneous rocks are non-porous and impervious (like granite) because the particles that make it are so tightly packed together.
Metamorphic rocks are formed when rocks become warm enough to bend or mould but not hot enough to turn into a liquid. Marble is a metamorphic rock formed when limestone becomes heated and squashed. Slate is also metamorphic and is formed from shale. Metamorphic rocks can sometimes form interesting shapes depending on how they have been ‘moulded’.
Rocks are weathered physically (by sun or heat and cold), biologically (by animals and plants) and chemically (by rain that contains chemicals that break the rocks down).
Erosion is the movement of rock fragments after weathering. Once rock has been eroded it gets washed away and may start to reform new sedimentary rocks. These sedimentary rocks can be change into metamorphic or igneous rocks after a long time, before the process of weathering starts again. This is called the rock cycle.
The type of soil found in any specific area is determined by the types of rock found in that region. The soil is a combination of a range of ingredients that include fine ground up pieces of rock; particles from dead plants and animals; air and soil. It is the amounts of each, in combination with the rock type and proportions of sand and clay that determines which soil type it is. There are three main categories of soil: sandy, clay or loam. Sandy soil is a dry soil with lots of air in it. Clay soil is sticky and doesn’t have much air in it. It tends to hold a lot of water. Loam soil is somewhere between clay and sand and so holds a bit of water, but not too much, and has a fair bit of air in it. Loam soil is generally the best type of soil for growing plants in.
Soil is also layered. If you dig right down you might go through six different layers, the last of which would be rock (often called bedrock). The first layer (O) is mainly organic matter – dead and decaying bits of plant and animal, while the second layer (A) is the topsoil. Topsoil is the part that we dig into in order to plant things. The eluviated layer (E) comes next (although this is not always there) and is quite sandy and clay filled. Then we find subsoil (B) and parent material (C), before hitting the bedrock (R). A soil sample that shows all of these layers (known as horizons) is called a soil profile.
Plants generally need soil to help them grow as it provides them with nutrients, air and water, as well as something the plants can anchor their roots into. The type of soil found in an area will determine which plants will grow naturally and thrive and those that won’t. Specific plants will grow best in specific soil – for example yukka plants like clay soils while lavender likes sandy soils. Most plants will grow well in a loam soil.
Soils also provide a home (or habitat) for a range of creatures. Earthworms and many bugs live in the soil while rabbits and moles, for example, dig their homes underground in the soil. Earthworms are important in the maintenance of soil as they aerate it (add air to it).
Words to know:
Bedrock: the solid rock that is found once you have dug through all the layers of soil.
Clay soil: soil that has a high proportion of clay.
Horizon: a layer of soil in a soil profile.
Igneous: a rock formed from magma either inside the Earth or on the surface.
Impermeable: cannot easily let water in.
Loam soil: a soil which is a fairly even mixture of sand, clay and silt.
Magma: liquid rock that is very hot.
Mineral: of a precise mix of chemical ‘elements’ which are organised in a very specific way.
Metamorphic: a rock formed when existing rock is changed through heat and pressure.
Non-porous: something that doesn’t have any gaps in it that water can get in to.
Organic material: dead or decaying matter found at the top of soil. This lies just on top of the topsoil.
Parent material: the broken rock from which a soil is formed. It is found at the bottom of a soil profile.
Peat: a dark soil that is mainly made from partly decayed plant material.
Permeable: can easily let water in
Porous: something that has gaps in it that water can get in to.
Rock: a solid formed of the particles of one or more minerals.
Rock cycle: the movement and recycling of rocks by nature. Rocks change from one type to another during this process.
Sandy soil: soil that has a high proportion of sand.
Sedimentary rock: rock formed when layers of mineral particles are squashed together
Silt: fine rock particles that are not as fine as clay, but not as coarse as sand.
Soil profile: the various layers if soil from organic matter on top to the bedrock at the bottom.
Topsoil: the first proper layer or horizon of soil which is found when you dig into soil.
Characteristics of materials - lesson plan
- To recognise simple properties of materials, such as strength, flexibility, transparency.
- To understand that materials are suitable for making a particular object because of their properties.
- Online activities:
- Learning Zone Broadband Class Clips:
- Other resources:
- Everyday items made from a range of different materials (metal, glass, paper, fabric, rubber, plastic)
- Large sheet of material
- Interactive whiteboard
- Cards showing the words 'waterproof', 'flexible', 'strong', 'transparent'
- Pictures of a tyre, a towel, a saucepan, a window, a notebook and a drink bottle
You will need Adobe Acrobat reader to access the PDF files. BBC Webwise has a complete guide to downloading and installing Adobe Acrobat reader.
- Watch Learning Zone Class Clips - Materials and their uses.
- Ask the children to get into pairs and list the materials from the clip and what they are used for.
- Recap on the fact that a material is the substance from which a thing is made (the word doesn't just mean fabric).
- Show the everyday items and ask the children what material each one is made from.
- Make a list of these materials on a large sheet of paper.
- Watch Learning Zone Class Clips - Which material?
- Pause and discuss how to keep the test fair. Discuss what the fairy godmother's results show. What did she do wrong?
- Place the four cards around the room (waterproof, flexible, strong, transparent). Make a statement such as "Does not let water through". Ask the children to run to where the correct word is (waterproof) to check their understanding of key scientific words.
- Play the Bitesize Characteristics of material activity. Explain that you are going to test each material to find out how it usually behaves.
- Drag the paper into the tester. Ask different children to come up to carry out one of the four tests. Ask them to predict what they think will happen.
- Ask if there are any other obvious properties the children could add (eg paper is light).
- Repeat this activity for the other materials.
- Click on the Workshop button in the Bitesize Characteristics of material activity. Show the children the blueprints for the tyre, towel, saucepan, window, notebook and drinks bottle. In pairs, ask them to predict a good material to make each object from, to explain why it would be a good material, and also to suggest a material it could not be made from and why. Ask the children to write their choices on the characteristics of materials worksheet (PDF 56KB).
- On the interactive whiteboard, use the Workshop to check the children's predictions.
- For each object, ask: What are its functions and what properties does it need? Which material has those properties? Which material would not be a good choice? Why?
- Ask the children to design an umbrella to keep off the rain.
- Ask them first to brainstorm a list of possible materials they could make it from.
- Explain that they should then go through the list and decide why it would not be sensible to make an umbrella from some of the materials.
- Alternatively, ask the children to complete the characteristics of materials worksheet (PDF 56KB).
- Ask the children to make four different designs for a cup, each made from a different material. Two of the designs must work and two of them must not work.
- Ask the children to explain why each of the cups will be a success or a failure.