These stones are made up of a lot of different minerals. Supposedly used in China as far back as the Ming dynasty for medicinal treatments. Today it is used to add minerals to improve water quality. It is mined in Japan and called Bakuhanseki which loosely translated I guess means barley and rice. Because it resembles a barley and rice ball.These look pretty consistent from stone to stone. Size is listed in the product title in millimeters (mm)
