Ask Ollie
Rock Detectives: Scratch and Streak Lab
Here's one to try together!
Scratch, streak and splash your way to ranking rocks from softest to hardest!
Reviewed by our team.
Safety first
- steel nail is sharp and must be held by a grown-up
- rocks may be rough or have sharp edges
- only collect rocks from places where it is allowed
- wash hands after handling rocks and dirt
What you need
- Water, 1 cup
- Clear cups, 1 (optional)
- Paper, 2 sheets
- Crayons or markers, 1 pencil
- Copper coin, 1
- Steel nail, 1, for a grown-up
- Tile, 1 old tile or rough paving slab
- Towel, 1 old towel, or a tray
How to do it
Grown-up prep: Gather rocks from a place where collecting is allowed, plus the tools below. Keep the steel nail for yourself, since only a grown-up holds it.
- Lay out your rocks and give each one a detective name.
- Try scratching each rock with your fingernail. Ask: Which rock do you think will be the softest?
- Now try scratching each rock with the copper coin.
- A grown-up holds the steel nail and scratches each rock. A grown-up does this
- Rub each rock hard across the back of the tile.
- Look at the streak line and note its color. Ask: Is the streak the same color as the rock?
- Wet each rock with water and look for sparkles or layers.
- Sort your rocks in a row from softest to hardest.
- Now show your friends, or hunt for more rocks! Which new rock might be the hardest? Ask: Which new rock do you think will beat every test?
Play it again
- Mystery rock: a friend picks a hidden rock and you test it to match it to your ranking.
- Rock museum: label your best rocks with names and notes, and display them on a shelf.
- Park patrol: take your tools to a new spot where collecting is allowed and compare the rocks you find.
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