
Scratch Testing and Rock Hardness
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Why can a diamond scratch glass but a fingernail cannot? Every mineral has a hardness rating on the Mohs scale (a ranking from 1 to 10). You can figure out a rock's hardness by testing what it can scratch.
You gather several rocks and common objects like a coin and a nail. Then you try to scratch each rock with each object. By recording which items leave a mark, you rank your rocks from softest to hardest.
Hypothesis
The hypothesis is that rocks of different compositions have different levels of hardness, and that the Mohs Scale can be used to classify and compare their relative hardness.
Method & Materials
You will test different rocks and minerals progressively with a fingernail, penny, iron nail, and steel file to see which object was able to make a scratch on the rock or mineral. Then compare the object that was able to make a scratch to the Mohs Scale to determine the rock or mineral's hardness level.
You will need samples of different rocks and metals, as well as an old copper penny, an iron nail, and a hardened steel file.
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See what’s includedResults
After conducting the "Rock Hardness Challenge," it was observed that different rocks and minerals have different levels of hardness. It is interesting to note that some rocks, such as granite, are much harder than others, like talc, which can be easily scratched with a fingernail.
Why do this project?
This science project is interesting because it teaches you how to use the Mohs Scale to test the hardness of rocks and metals. It also shows how geologists and miners use the Mohs Scale to classify and compare different minerals in their work.
Also Consider
Experiment variations could include testing the hardness of different types of rocks or metals, or testing the effects of different pressures or angles on the scratching process. Another variation could be testing the hardness of different household items using the Mohs Scale.
Full project details
Additional information and source material for this project are available below.Related video
These videos explain the science behind this project and demonstrate key concepts used in the experiment.
Discover the history of the Mohs hardness scale and learn about the ten rocks and minerals that are ranked from softest to hardest! Can you guess which rock is the softest and which one is the hardest? Let's find out!
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