Iolite is the gem-quality blue or blue-violet variety of cordierite. While iolite enjoyed popularity in jewelry in 18th-century Europe, this naturally beautiful gemstone is relatively new to the jewelry market and is regaining popularity with the public. Because of its hardness and pleochroism, iolite is one of the most difficult stones to cut. It must be cut in a certain direction to take advantage of the best color, which can be tough when the shape of the rough doesn't lend itself to cutting in that same direction.