All lessons › Challenge: Rock cycle detectives › Lesson 3
Australian primary science · Years 5–6 (challenge) · Lesson 3 of 3
The crayon rock cycle
Inquiry question: How can crayons model the way rocks change from one type to another?
Check practical materials
Using a model
What students learn
Weathering, deposition, compaction, heat and pressure, melting and cooling change rocks from one type to another. A crayon model shows these steps, but it has limits we must explain.
Success criteria
- I can use crayons to model sedimentary, metamorphic and igneous rock.
- I can link each step of the model to a real process.
- I can explain two ways the model is not like real rocks.
Preparation and materials
Before this lesson: Students know the three rock types and how they form (lessons 1 and 2).
- Old wax crayons, paper peeled off, 3 colours per pair — 39 (3 per pair)
- Plastic pencil sharpeners or blunt plastic knives (to make shavings) — 13
- Aluminium foil squares, about 20 cm × 20 cm — 26 (2 per pair)
- Paper plates — 13
- Heavy books for pressing — 13
- Bowl and a kettle of very hot water (teacher only, for the melting demonstration) — 1
- Small foil cupcake cases or a foil ‘boat’ for melting — 2
Teacher setup
- Peel crayons beforehand and test that the sharpeners make shavings.
- Place the kettle and bowl on the teacher’s bench, out of students’ reach.
- Make one example of each ‘rock’ to show if time is short.
Safety and adaptations
- Only the teacher handles the kettle and hot water. Students stay at their tables during the melting demonstration.
- Shave crayons away from your body, and keep fingers clear of the blade.
- Don’t eat crayon, and wash hands afterwards.
Review your school policies and curriculum requirements before teaching.
How to investigate
The lesson sequence should leave pupils with evidence to interpret, not only an activity to finish.
- Pairs make shavings of three colours (weathering and erosion).
- Sprinkle the colours in layers on a foil square (deposition).
- Fold the foil and press gently with your hands: open it and record (sedimentary rock).
- Fold it again, warm it in your hands for a minute, then press very hard under a heavy book: record (metamorphic rock).
- Watch the teacher melt a sample in a foil boat floating on very hot water, then let it cool (igneous rock).
- Write two ways the crayon model is like real rocks and two ways it is not.
Teacher modelling prompt
Shave a little crayon onto foil. Think aloud: “These shavings are like sediment from weathering. If I layer three colours and press them with my hand, I get a crumbly ‘sedimentary rock’ with layers. Now I fold the foil and press very hard with a heavy book, and warm it in my hands: it bends and smears without melting. That’s like metamorphic rock.” Explain that you will do the melting step yourself.
Record and explain evidence
Recording question: How can crayons model the way rocks change from one type to another?
| Step | What we did to the crayon | What it looked like | Real rock process | Real rock type |
|---|---|---|---|---|
| ________________ | ________________ | ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
What can and can’t a model show us?
Check understanding
What should pupils know? Describe how a sedimentary rock could become an igneous rock.
Explain with evidence: Explain one limitation of the crayon model and why it matters.
Apply the idea: Fossils are found in sedimentary rocks but almost never in igneous rocks. Use the rock cycle to explain why.
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.