Lesson focus: Which clues help us identify a rock?
Use observations to support a rock classificationSorting living things into groups based on what they have in common. and acknowledge uncertainty.
Build on earlier learning
Evaluating dataMatch the strength of a conclusion to the available evidence.
Practical
Identifying rocks
- Look for grains or crystals with a hand lens.
- Drop water on the rock to test whether it is porous.
- Add dilute acid to test for carbonate (fizzing).
- Use a key to name the rock type.
Record: A table of each test result and the rock type it supports.
Safety: Wear eye protection when using acid.
You will be successful when you can…
- Describe texture objectively.
- Link features to possible processes.
- Request discriminating evidence.
- Express uncertainty appropriately.
Words that carry the science
- grain
- Individual fragment or mineral particle in a rock.
- interlocking
- Fitting together with boundaries that meet closely.
- fossil
- Preserved remains or trace of a past organism.
- banding
- Layers or stripes of different minerals or textures.
- classification
- Grouping using shared evidence-based characteristics.
Move from observation to a qualified rock identification
01Observe before naming
Record grainOne small piece or particle in a rock. shape, size, sorting, crystals, layers, fossilThe remains or traces of a living thing from long ago, preserved in rock., pores and bands without first forcing a rock name.
02Infer possible processes
Rounded cemented grains support transport and lithification; interlockingFitted tightly together with no gaps, like jigsaw pieces. crystals support crystallisation; aligned bands can support directed pressure and metamorphism.
03Test alternatives
Colour varies within rock groups. Interlocking crystals occur in igneous and metamorphic rocks, so composition, contacts and other textures matter.
Classify with two observations
A sample has rounded sand-sized grains cemented together and a shell fragment.
- State observations without interpretation.
- Rounded grains are consistent with transport.
- Cement supports lithification; shell material can be preserved in sediment.
- Suggest sedimentary and request layering/context to strengthen confidence.
How to make the reasoning visible: The classificationSorting living things into groups based on what they have in common. is justified but remains open to further evidence.
Evidence matrix
Treat the figure panels as diagrams, not photographs.
| Observation | Possible group | Formation link | Extra check |
|---|---|---|---|
| Rounded cemented grains | Sedimentary | Transport + lithification | Layering/fossils |
| Interlocking crystals | Igneous or metamorphic | Crystallisation | Composition/context |
| Aligned mineral bands | Metamorphic | Directed pressure/recrystallisation | Mineral alignment |
| Single dark colour | Any | Not diagnostic | Texture/hardness |
Why is colour weak evidence?
What does a scale bar add?
Use the matrix. Why is a single dark colour not enough to identify a rock?
Check your understanding
Answer from memory, then check against the suggested answer.
What is grain?
What is interlocking?
What is fossil?
Which rock type often has visible layers or fossils?
Which rock types usually have interlocking crystals?
A rock has interlocking crystals. Why not immediately call it igneous?
How would you distinguish a conglomerate from a similarly coloured crystalline rock?
A rock fizzes when a drop of dilute acid is added. What does this suggest? (Wear eye protection.)
Exam Question Practice
Exam Question Practice
Mark points shown after marking
A rock contains rounded grains and a shell fossil. Suggest its rock group and justify your answer.
(4)Total for this question: 4 marks
Command word: A strong identification pairs each observation with a formation process.