Much of the earth’s crust is made of rock. All rocks are made of minerals. Some rocks are made of several minerals, while others are made of just one kind of mineral.
One way that minerals are identified is by their hardness. Diamond is the hardest mineral; talc is the softest. To determine the hardness of a mineral, a scratch test is used. The mineral can then be identified using the Mohs Hardness Scale shown below. Each mineral on the scale can scratch any mineral that has a lower number than it on the Hardness Scale.
| Hardness Number |
Scratch Test |
Mineral |
| 1 |
Fingernail scratches it easily |
Talc |
| 2 |
Fingernail barely scratches it |
Gypsum |
| 3 |
Copper penny just scratches it |
Calcite |
| 4 |
Steel knife scratches it easily |
Flourite |
| 5 |
Steel knife barely scratches it |
Apatite |
| 6 |
Scratches glass easily |
Feldspar |
| 7 |
Scratches steel & glass easily |
Quartz |
| 8 |
Scratches all other common minerals |
Topaz |
| 9 |
Scratches topaz |
Corundum |
| 10 |
Hardest mineral |
Diamond |
Amanda enjoys collecting rocks and minerals. Among the samples in her mineral collection are Quartz, Gypsum, Diamond, Fluorite, and Topaz. One day, Amanda accidentally dropped the small tray that she used to display these five minerals. When she dropped the tray, the labels for the samples got mixed up. To figure out which sample was which mineral, she devised an experiment. She labeled the rocks A, B, C, D, and E, and tested the minerals to see which samples scratched which other samples. She recorded the following results:
Mineral A scratches mineral D but not C.
Mineral C scratches mineral E but not B.
Mineral E scratches mineral D but not A.
Can you help Amanda figure out which sample is which mineral?