What Kind of Rock Is This?
ES0610  Coarse-Grained Igneous Rocks

  !   Read the questions below each image.

Matthew Nyman, TERC

Is the rock generally light colored with dark crystals spread throughout? If yes, your sample is probably granite. Granite usually takes on the color of the feldspar crystals in it.

Matthew Nyman, TERC

Is your rock dark colored? If yes, your sample is probably gabbro. Due to the dark color of gabbro, individual minerals may be hard to see. Look for crystal surfaces that reflect light.

Matthew Nyman, TERC

Does your rock have roughly the same number of light and dark crystals, or appear a gray color overall? If yes, your sample is probably diorite.

If you have identified your sample, return to the beginning of the rock identification key, select another rock sample, and begin the process over again.

If your rock sample does not have any of the features described on this page, reexamine the rock with a hand lens or magnifying glass. Look at the sample from all angles. Concentrate on fresh surfaces where you might be able to better determine the texture. Return to the beginning of the rock identification key and start over again.