Táo(hé)yàn) are made from the stones found at the bottom of the Tao River in Gansu Province. These inkstones were first used during the Song Dynasty and became rapidly desired. It bears distinct markings such as bands of ripples with varying shades. The stone is crystalline and looks like jade. These stones have become increasingly rare and are difficult to find. It can easily be confused with a green Duan stone, but can be distinguished by its crystalline nature.