Hobbies And Interests

How to ID Rocks

Rocks and minerals exist all over planet Earth, with some types more prevalent than others, primarily Basalt, an igneous rock, which composes two-thirds of the Earth's crust. A mineral is a single component of a rock, while a rock is a combination of two or more minerals. They form the Earth's crust. There are three types of rocks on Earth, sedimentary, igneous and metamorphic. Igneous rocks form when magma cools; sedimentary rocks form when particles of other rocks, plants and animals are exposed to pressure over time; and metamorphic rocks form when either an igneous or sedimentary rock is exposed to great pressure and/or heat together over time.

Things You'll Need

  • Magnifying glass
  • Piece of steel
  • Field guide to rocks and minerals
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Instructions

    • 1

      Examine the layers of the rock. If it can be split into multiple layers, you likely have a sedimentary rock. An igneous rock is typically smoother and doesn't chip or split into layers. A metamorphic rock can be either originally sedimentary or igneous, so can be thus classified as one or a combination of the two.

    • 2

      Check the size of the grains. Large, coarse grains are easy to identify and make it simpler to note what minerals make up the rocks. Smaller grains are not visible to the naked eye and make it more difficult to identify the minerals. You may even need to use a microscope to note the size of the grains and crystals.

    • 3

      Identify the color of your rock. Look closely to examine all colors, not just the predominant one. Look for streaks and specs.

    • 4

      Test the hardness of your rock. Try to scratch your rock with your fingernail. If it scratches, the hardness is low. Then try to scratch the rock with a piece of steel, as well as the steel with the rock. Rocks that are hard, with a 6 to 7 rating on a scale from 1 to 10, can scratch glass and steel. Minerals are rated on Moh's scale of hardness, and knowing how hard a rock is allows you to know what minerals are in it, making it easier to identify.

    • 5

      Compare the characteristics you noted with a rock identification table, chart or book to figure out what type of rock it is and what the minerals inside it are. Using the rock identification chart, look at the rock's composition. If you have a rock with layers and fine grains, you can determine that it's a sedimentary rock by checking the chart. Determine its hardness as hard or soft, a classification usually found near the end of the chart. To identify your rock, follow the chart from one side to the other until you reach the end.


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