What is a Rock?

The word rock means different things to different people. As with many words, its scientific meaning is different from many of the meanings used in everyday language, so lets start with a short video on the scientific definition of a rock.

Notice that the definition of a rock is much shorter than the definition of a mineral. You only have three questions to answer to know if something is a rock or not.

  1. Is it naturally occurring?
    This simply means that it is not man-made. Even though it is made from minerals, concrete is not a rock because it is not naturally occurring.
    Learn more about what "naturally occurring" means.
  2. Is it a solid?
    The substance is not a liquid, gas, or plasma. Rocks can be made up of many small pieces of solid material, and those pieces don't have to be cemented together.
    Learn more about what "solid" means.
  3. Does it form large deposits in the Earth?
    Are there large layers or geologic structures made up of this substance? Natural solids that do not form large structures, such as diamonds and gold, are not rocks.
    Learn more about what "large deposit" means.

If the answer to all three of those questions is "yes", then the substance is a rock. To practice that, try putting it all together.