Rai stones are giant stone disks that we can find in the island of Yap, Micronesia and that are still used as currency,for some large transactions on the island. Rai were made out of limestone that don't exist in the island. The limestone is from the caves of Palau, 250 miles away.
We can find the stone money around the island, sometimes in groups, in different sizes, what we may call a "bank".
They can reach 3 meters (10 ft) in diameter, 0.5 meters (1.5 ft) thick and weigh 4 metric tons (8,800 lb). The largest piece is over 12 feet tall and cannot be seen because it's on the island of Rumong, which is closed off to outside visitors.
It's not only the size that gives the value to one piece, the type of rock, the shape and the piece's history are the factors of their worth. Other important factors are the difficulty in quarrying the stone, the arduousness of the sea journey in transporting it and the tools used to shape it.