Scientists often use properties to distinguish items or groups of items. Students who are studying minerals can make a mineral hardness scale to determine mineral’s resistance to being scratched. Mohs’ hardness scale is used for this purpose. A mineral on this scale with a higher number can scratch a mineral with a lesser number:
- 1 = Talc
- 2= Gypsum
- 3 = Calcite
- 4 = Florite
- 5 = Apatite
- 6 = Orthoclase
- 7 = Quartz
- 8 = Topaz
- 9 = Corundum
- 10 = Diamond
These might not be things you have sitting around the house, so you can use some common items to determine where something is on the scale:
- Lead Pencil = 1
- Chalk = 2
- Fingernail = 2.5
- Penny = 3
- Common Nail = 5
- Knife = 5.5
- Glass = 6
- Steel File = 6.5
- Flint Sandpaper = 7
- Emery Sandpaper = 9
So you can test a variety of items to determine how hard they are relative to each other. For example, if you can make a scratch on an item with a common nail, but not with a penny, you know it falls somewhere between 3 and 5 on the scale. You might find a magnifying glass helpful when doing the test so you can look closely for a scratch.
This could be the basis for a collection type science fair project. Collect a group of rocks and similar items and then group them according to their relative position on the hardness scale.
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