Bi-color tourmaline is a type of tourmaline gemstone that displays two distinct colors within a single crystal. These color zones can be sharply defined or gradually blend into each other, creating a beautiful contrast. The colors typically range from shades of green, pink, blue, or yellow, often arranged in vertical or horizontal bands. The most popular bi-color tourmalines are those with a combination of green and pink, but they can also feature combinations like blue and green, or purple and blue.

The formation of these color zones is due to varying chemical compositions during the crystal's growth process, with elements like iron, magnesium, and manganese influencing the colors. Bi-color tourmaline gemstones are prized for their unique and vibrant appearance, making them popular in jewelry such as rings, earrings, and necklaces.