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    Home / Science lessons / Mohs Hardness: Testing Rocks & Minerals
    • Mohs Hardness: Testing Rocks & Minerals

      There are many tests you can perform to help you identify your rock and mineral specimens. Our mineral test kit contains everything you will need for these tests. The first step is to examine your specimen with a magnifying glass and take note of its outside appearance. Look for the mineral's transparency. If you can see through the specimen, it is transparent. If light can pass through, but the specimen cannot be seen through, your mineral is translucent. Minerals that do not let light through are called opaque.

      Next, test your specimen for hardness. Mineral hardness is measured on the Mohs Hardness Scale. In the early 1800s, Friedrich Mohs used common minerals to invent a scale for comparing the hardness among rocks. On each level of the scale a mineral can be scratched by something of the same or higher level, but nothing lower. Number one on the Mohs scale is talc, because it is soft and very easy to scratch. Number ten is the diamond, because it is the hardest natural substance and can only be scratched by another diamond. Test your mineral specimen by trying to scratch it with your fingernail. Next try a copper penny, and then a steel nail. A fingernail has a hardness of 2.5, a penny is 3.5, and a steel nail is 5.5. If you are able to scratch your specimen with your fingernail but not with the penny, it has a hardness between 2.5 and 3.5. Also try scratching your specimen with another rock to see which one is harder.

      One last test that is commonly used is called a streak test. A mineral's 'streak,' or color when it is finely powdered, is always the same, even when the color of the mineral varies. (The streak can be very different from the color of the mineral itself.) Rub your specimen across a piece of porcelain tile (called a 'streak plate') and examine the color it leaves behind.

      Once you have performed your tests, compare your results with a rocks and minerals field guide to come to a final identification of your specimen.

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