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How do you identify the rocks that you find? Ed looks closely at the fine grains of a rock.
Ed looks closely at the fine grains of a rock.
   
Chuck Said
Some rocks are easy to identify. For example, sandstone is made of little tiny grains of sand all stuck together. It's pretty easy to spot a sandstone. Lavas are usually easy to identify. They have very, very fine grains, they may have bubbles in them, and they may have surface textures that suggest that they were liquid at one time. Granites are easy rocks to identify, too, because the mineral grains in them are large and easy to see.

But there are many rocks that are difficult to identify, especially rocks that have experienced stress from high pressures and high temperatures and have changed due to those conditions. Sometimes even geologists have difficulties identifying rocks. We use microscopes and chemical tests to show us what we can't see with our eyes.