S3.11.1 For the adult
Three kinds of rock
Why do some rocks sparkle and others crumble?
What this chapter teaches
A rock is described by its grains, its colour and its hardness. Hardness is tested by scratching: a harder thing scratches a softer one. Rocks are sorted by how they formed: igneous from cooled melted rock, sedimentary from pressed bits, metamorphic from rock changed by heat and pressure.
Three questions to ask
There is no one right wording. Listen for the idea.
- How would you describe a rock you can pick up near your home?
- Which tool scratched the rock first, and what does that tell you?
- Why is colour a poor way to sort rocks?
After the chapter, the learner can
- Describe a rock by its grains, colour and hardness
- Test the hardness of a rock by scratching it with a nail and a coin
- Sort rocks into igneous, sedimentary and metamorphic by how they formed
What they copy into their notebook
Igneous rock cooled from melted rock. Sedimentary rock is bits pressed together. Metamorphic rock was changed by heat and pressure. A harder thing scratches a softer one.