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“Hard Rock” Scratch Test

One characteristic of a rock or mineral is its hardness. In 1822, a famous scientist named Friedrich Mohs developed a scale to measure the hardness of minerals. The Moh’s scale, shown below, lists ten minerals from softest (talc) to hardest (diamond). A mineral will scratch other minerals softer than itself and will be scratched by minerals that are harder.
Follow the instructions below to test the hardness of one of your favorite rocks

Moh’s Scale of Mineral Hardness

Relative Scale

Mineral Hardness of Some
Common Objects
Hardest                   10 Diamond  
                                 9 Corundum  
                                 8 Topaz  
                                 7 Quartz  
                                 6 Potassium feldspar 5.5 Glass, Pocketknife
                                 5 Apatite  
                                 4 Fluorite 3.5 Copper Penny
                                 3 Calcite 2.5 Fingernail
                                 2 Gypsum  
Softest                       1 Talc  

Materials:  a rock, a penny, a butter knife (not plastic), a glass jar, and a journal


1.    Place a rock, a penny, a butter knife, and a glass jar on a table.

2.    Make a hypothesis about which items are harder than your rock and which are softer. 

3.    Record your hypothesis in a journal.

4.    To test the hardness of your rock, try to scratch a penny, a knife, and a glass jar with your rock. 

5.    In your journal, record what items your rock scratched and what items it did not scratch. 

6.    Next, try to scratch your rock with your fingernail, a penny, and a knife.

7.    Record the results in your journal.

Use the data you collected during the scratch test, to make a conclusion about what items are harder than your rock and which items and softer.