Is it a clay? Is it a sandy mud? It's not clay and it's not sandy mud. It's a special kind of rock which is mostly mineral deposits found under the ground near Yixing city. Nowadays the rock after it's mined are grounded by the machine with water, then it's filtered. The paste (just like the bean paste) is then used to make the teapots and cups. This paste is called Zisha Sand,because it contains very fine sandy particles. It's all because of this special format of mineral paste that made Zisha Yixing teapot so famous and fine craftsmen's teapot are sold easily and well over 10,000 yuan in China.