Tourmaline Gemstones and Jewelry
Tourmaline is a boron silicate gemstone that may contain any of a number of other elements, giving it a chemical formula of (Ca,K,Na,[])(Al,Fe,Li,Mg,Mn)3(Al,Cr, Fe,V)6
(BO 3)3(Si,Al,B )6O18(OH,F)4. It forms trigonal crystals and has a hardness of 7 to 7.5. Tourmaline is often black but may be colorless, red, green, bi-colored, tri-colored, or other colors. Citation
