Rock detectives
Rocks are made of tiny bits called minerals. Meet the three kinds of rock, find out how rocks slowly break and change, and be a rock detective with a magnifying glass and a drop of water.
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A rock is hard and solid. It is made of tiny bits called minerals.[1]
There are three kinds of rock: igneous, sedimentary and metamorphic.[1]
Igneous rock is made when very hot, melted rock cools down and goes hard. Granite and basalt are igneous rocks.[1]
Sedimentary rock is made of little pieces of other rocks, like sand and mud, that pile up in seas and lakes and get pressed together. Limestone can even be made from old shells![1]
Metamorphic rock is rock that was buried deep down, where it got very hot and was squeezed hard. It changed into a new rock: limestone can become marble.[1]
Rocks slowly break. Water in a crack can freeze and push the crack open. Plant roots can grow in a crack and make it wider.[3]
Rocks can change from one kind into another, but very, very slowly: it takes millions of years.[2]
Try it: Rock detectives
You need
- 3 or 4 different rocks (for example granite, sandstone, slate, a beach pebble)
- A magnifying glass
- A dropper or teaspoon and a cup of water
- Paper towels
Safety
Do not bang or break the rocks: chips can fly into eyes. Do not put rocks or water in your mouth. Wash hands afterwards.
What to do
- Look at each rock with the magnifying glass. Can you see shiny crystals, small grains like sand, or flat layers?
- Feel each rock. Is it rough or smooth?
- Guess: will a drop of water soak into the rock, or stay on top?
- Put one drop of water on each rock and watch for one minute.
- Which rock drank the water? Which rock kept the drop on top?
Play: Rock or not?
Is it a rock? Tap the right group.
Your best score is kept only on this device. Nothing is sent anywhere.
Quiz
Other ages: Ages 10–11 · Ages 15–16