Mysterious material

Activity overview

Run the activity

You will be zooming in and out of the image above – starting very close and stepping back slowly.

1. Start by asking everyone:

• What do they think the image is and why?
• What does the image remind them of and why?

2. Every time you zoom out, ask the class:

• Can they describe the colours, shapes and textures?
• What do they think the image is now – have they changed their minds?

Background science

Chalk is a soft, whiteish rock and is a type of limestone. It is normally formed underwater, commonly on the sea bed, mostly from the skeletons of tiny sea creatures, called coccoliths. It takes many years to form.

Chalk is very porous, which means that it can soak up and store water. When chalk is next to the sea, the water does not wear it away easily and often makes a large cliff or chalk hills. The White Cliffs of Dover and the Seven Sisters are well known examples found by the English Channel.

Take it further

What other rocks can you name? There's a great selection of BBC clips showing rocks in a variety of forms. Children could identify a set of rocks by looking closely at their appearance. With sedimentary rocks children should be able to see grains in layers, whereas igneous rocks have randomly arranged crystals. Metamorphic rocks are often crystalline, and some have visible bands. Children could use this key to identify their rocks. Science Sparks has a series of tests children can do to identify different properties. 

Which of these rocks are porous too? You can test a rock’s porosity by dripping water onto it and seeing how much is absorbed. You can also put a sample of rock into a cup of water and count the bubbles that appear. Rocks with the most bubbles have spaces between the grains so that air and water can flow through.

Find out more about pebble beaches with this Big Question: Why don't all rocks look the same? or tfind out more about fossils by asking the class What if fossils didn't exist?