What it shows
Crayon shavings pressed together act like sediment turning into sedimentary rock, pressed and warmed they become metamorphic rock, and melted and cooled they become igneous rock. The same changes, with real heat and pressure over millions of years, make up the rock cycle.
The science
Sedimentary rock forms when loose grains are buried and pressed until they stick; the cold-pressed shavings show that. When rock is buried deeper it is squeezed and warmed without melting, and its grains flatten and bands form, which is metamorphism. If it goes deeper still it melts to magma, and when magma cools it crystallises into igneous rock. Rocks of any type can weather back into grains, and the cycle starts again.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Three old wax crayons of different colours
- A pencil sharpener or a plastic knife for shaving
- Aluminium foil folded into small cups
- A bowl of hot water from a kettle
- A heavy book
- Paper towels
Safety
For this project: An adult must pour the hot water and handle the foil cup while it floats. Do not use a flame or a microwave for the wax.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
9 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Shave each crayon into a separate pile; these are the weathered grains.
Mix a spoon of each colour loosely in a foil cup and look at it; this is loose sediment.
Fold the foil closed and press it hard under the heavy book for two minutes.
Open it: the shavings now hold together in layers, like sedimentary rock.
Wrap the lump in fresh foil, float it on hot water for one minute, then press it under the book again.
Unwrap and observe that the colours have smeared and flattened into bands, like metamorphic rock.
Put the lump in a foil cup and let it float on fresh hot water until it fully melts.
Lift the cup out with tongs, let it cool, and observe the smooth mixed solid, like igneous rock.
Draw the cycle with arrows and paste a small sample from each stage beside its name.
What you should see
Three samples that look clearly different: a crumbly layered lump, a flattened banded lump and a smooth solid disc, mounted on a rock cycle diagram.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Which stage needs no heat?
Sedimentary rock, which forms by pressure alone.
2What is the difference between metamorphic and igneous?
Metamorphic rock changed by heat and pressure without melting; igneous rock cooled from a melt.
3Give an Indian example of each rock type.
Sandstone of the Red Fort, marble of the Taj Mahal, basalt of the Deccan plateau.
4What turns rock back into grains?
Weathering and erosion by water, wind and temperature changes.
Take it further
Repeat with sugar instead of wax under adult supervision and compare how the crystals look after cooling.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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