Bead, Tourmaline (natural), 5mm Smooth Heishi Cube, A- grade, Mohs hardness 7. Sold per 14-inch strand - Tourmaline (tur-mah-Leen) is a crystal boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gemstone comes in a wide variety of colors.