Testing the Hardness of Minerals Hardness is a useful way to help identify your mineral finds. The Mohs Hardness Scale, below, ranks some common minerals in terms of hardness, or how easily they can be scratched. Talc Gypsum Calcite Fluorite Apatite Orthoclase Quartz Topaz Corundum Diamond Talc, the lowest mineral on the scale, is so soft you can scratch it with your fingers. Diamond is famous for being one of the hardest minerals, and for good reason: almost no natural substances can scratch it. Making your own hardness test kit is a good way to start learning hands-on, and determining a mineral's hardness is a good clue for identifying the type of mineral you have. The way the scale works is simple. Any material lower on the scale can be scratched by those above it. So gypsum can scratch talc (but talc can't scratch gypsum).
Similarly, calcite can scratch gypsum and talc but not fluorite. Find a mineral (not a rock). Try to scratch it with these common items: Fingernail: 2.5 A real piece of copper: 3 (not a penny; they aren't made of much copper anymore) Steel nail: 5.5-6 (for safety, have an adult help you) A piece of quartz: 7 To scratch it, hold the to-be-scratched mineral firmly in one hand. Use a pointed area of the "scratching" item and press firmly, away from your body/fingers. If it leaves a scratch-mark, the mystery mineral is softer than the "scratching" item. Start with your fingernail.
If it leaves a scratch, then your mineral is softer than 2.5 on the scale. If it doesn't leave a scratch, try the piece of copper, and so on. Once you've found something that scratches it, you're close to figuring out its hardness. After that, it's often a matter of scratching it with other minerals from the chart (or your scratching tools). Seeing if you can narrow down a more specific range. For example, if your fingernail doesn't scratch it but a piece of apatite does, then you know the hardness is between 2.5 and 5.
Once you have an approximate hardness, you can search online for minerals in that hardness range.