Rai stone（萊石）

Rai stone [finance.qq.com]

If you go to the Island of Yap – part of the Solomon Islands -- you may find the world's largest and weirdest form of currency: The Rai stone. The Rai stone is a limestone disk with a hole in the middle. It measures 12 feet in diameter and weighs up to eight tons. It is probably the only currency in the world that can not fit into your average pocket. As a currency, the Rai stone does not circulate on the market, instead, it stays where it is, although its owner changes from time to time. Everyone on the island knows who owns the stone.