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A rock is a solid collection of minerals. Granite is mostly the minerals quartz, feldspar and mica, as crystals locked together. Sandstone can contain the same minerals, but as grains cemented together.

Igneous rocks form when magma cools. Lava that cools fast at the surface makes rock with small crystals, such as basalt. Magma that cools slowly underground, maybe over thousands or millions of years, makes rock with large crystals, such as granite.

Rocks are broken down by weathering. Water freezes in cracks and the ice pushes them apart; rain is slightly acidic and slowly changes minerals; roots and burrowing animals widen cracks.

Experiment: Sugar-cube river: shaking and wearing

1. Put 4 sugar cubes into each jar and close the lids.
2. Plan a fair test: what will you change, and what will you keep the same? (Change the number of shakes; keep the same cubes, jars and shaking strength.)
3. Predict: what will the cubes look like after 50, 100 and 200 shakes?
4. Shake jar 1 50 times, jar 2 100 times and jar 3 200 times.
5. Tip each jar through the sieve over the dark paper. Look at the cubes and at the powder that falls through.
6. Count the sharp corners left on the cubes in each jar, and compare the amount of powder.

Jar	Prediction	Sharp corners left	Amount of powder (little / some / lots)
50 shakes
100 shakes
200 shakes

Questions

1. Draw the rock cycle with three boxes: igneous, sedimentary and metamorphic. Add arrows and label them with words like cooling, weathering, erosion, deposition, heat and pressure.

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2. What happened to the cubes as you shook them more times? How did you keep your test fair?

3. Why does granite have bigger crystals than basalt?

4. What is the difference between weathering and erosion?

Sources for every fact on this sheet: echoesof.science/school/rocks/sources/

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