Tourmaline is a rare silicate mineral that is found in pegmatites in several countries. It comes in all the colors of the rainbow. The terms 'bicolor' and 'tricolor' refer to the unusual phenomenon when the same crystal changes colors along its length. 'Watermelon' Tourmaline is when a crystal has an internal red core and a green exterior, so when it is sliced it resembles the fruit. Tourmaline is found primarily in Brazil, Afganistan, and Nigeria. It is also found in California, Maine, Pakistan, Nepal, and Madagascar.