Testing a rock like a scientist
How do experts decide whether a rock is a meteorite? They look for several clues, use simple fair tests and only then ask a specialist laboratory. This lesson shows you the clues.
- List the main clues that a rock might be a meteorite.
- Carry out a fair comparison of how heavy two rocks are for their size.
- Explain why scientists need several pieces of evidence.
Links to: Year 3 science, rocks: comparing rocks by appearance and physical properties; working scientifically: fair tests, observations and conclusions.
The clues
Meteorite scientists look for several clues together:
Heavy for its size. Metal makes most meteorites feel heavier than an Earth rock of the same size.
A fusion crust. A thin dark skin, sometimes with tiny cracks, made during the fiery fall.
Thumbprint dents. Some meteorites have shallow dents like thumbprints in clay, called regmaglypts, carved by the hot air.
Attracted to a magnet, because of the metal inside.
No bubbles. Meteorites are solid. A rock full of small holes is usually slag or lava from a volcano.
The streak test
Rub a corner of a rock on the back of a white bathroom tile, the rough unglazed side. Some minerals leave a coloured line called a streak. Haematite, a common iron ore, leaves a red-brown streak. Magnetite leaves a black streak. Most meteorites leave no streak or only a very faint grey one. A strong red-brown or black streak means the rock is almost certainly from Earth.
Evidence, not guesses
One clue is never enough. A real scientist collects several clues and asks whether they all point the same way. Even then, the only way to be sure is for a specialist laboratory to look at a tiny piece under a microscope and measure what it is made of.
If you ever find a rock you think is a meteorite, do not cut it, heat it or put acid on it. Photograph it, note exactly where you found it and ask an adult to contact a museum or university.
A fair test: which rock is heavier for its size?
Two rocks are about the same size as a tennis ball. Rock A weighs 340 g. Rock B weighs 1,020 g. How many times heavier is rock B?
- To find how many times heavier, divide: 1,020 ÷ 340.
- Try multiplying 340 by small numbers: 340 × 2 = 680 and 340 × 3 = 1,020.
- The test is fair because the rocks are the same size, so only their mass is being compared.
Answer: Rock B is 3 times heavier for the same size, so it probably contains a lot of metal. It could be an iron meteorite, or iron ore or slag, so more clues are needed.
Try the streak test on any rocks you have, using the back of a white tile. Record the colour of each streak in a table. Then use the Is my rock a meteorite? checker on this site to go through the clues one at a time for an imaginary rock.
Quiz
5 questions. Choose an answer to see whether you are right and why. Finish the quiz to complete the lesson.
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Question 1Which clue suggests a rock could be a meteorite?
Most meteorites contain metal, so they feel heavier than an Earth rock of the same size. Bubbles and a red-brown streak point to Earth rocks.
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Question 2What are regmaglypts?
Hot air streaming past a falling meteorite can carve shallow dents into its surface that look like thumbprints in clay.
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Question 3A rock leaves a red-brown streak on a white tile. What is it probably?
Haematite leaves a red-brown streak. Most meteorites leave no streak or only a faint grey one.
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Question 4Why is a fair test important when comparing how heavy two rocks are?
If the rocks are different sizes, a bigger rock might be heavier just because it is bigger. Keeping the size the same makes the test fair.
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Question 5You find a rock you think is a meteorite. What should you do?
Testing by cutting, heating or using acid can spoil a meteorite and is unsafe. Experts can check it properly.