Indicolite 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 Dark blue tourmaline is called indicolite , or indigolite . These are some of the most beautiful and sought after tourmaline s. Enhancements Green and Blue tourmaline is commonly heat treated to improve color. More information on gemstone enhancements. Heated to improve color.