This is a type of igneous rock which is quarried on the coast of Itoigawa City in Niigata Prefecture. In Chinese medicine, the stone is called "Tora ishi" and has been used in medical treatments since ancient times. There is a legend among the local people that recommends holding this stone, the himekawa yakuseki, when you are in bad physical condition, because it can improve one's immunity. Since it contains radioactive elements such as a tiny amount of radium and thorium, it generates radioactive gases such as radon and thoron. It is believed that the stone can induce Hormesis effects (an adaptive response that allows the creation of resistance to specific substances), leading to improved immunity to various ailments.