Bead, Tourmaline (Natural), 4mm smooth Roundel B- Grade, Mohs Hardness 7, Sold Per 5 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.