Watermelon Tourmaline Gemstones Hardness 7.0. Tourmaline and opal are the birthstones of the month of October.
Tourmaline is the national gemstone of the United States.
Appearance Long tourmaline crystals often form with different colored layers. Watermelon tourmaline is named by the slices which are formed when these crystals are cut. Watermelon and Bi-color tourmaline s are normally quite included. Enhancements Occasionally heat treated to improve color. More information on gemstone enhancements.