|Tourmaline Crystals. Sapo Mine, Ferruginha, Conselheiro Pena, Doce Valley, Minas Gerais, Brazil|
Credit: Heritage Auctions
Tourmalines are boron silicate minerals that get their rainbow-like colors from various elements such as iron, sodium or magnesium. Tourmaline is classified as a semi-precious stone and the gemstone comes in a wide variety of colors.