Rai Stones from Yap

(from Wikipedia)

Rai stones are circular disks with a hole in the middle. The stones vary widely in size: the largest are 3.6 meters (12 ft) in diameter, 0.5 meters (1.5 ft) thick and weigh 4 metric tons (8,800 lb). The largest rai stone is located on Rumung island, near Riy village.  Smaller rai stones might have a diameter of 7–8 centimetres.
The extrinsic (perceived) value of a specific stone is based not only on its size and craftsmanship, but also on its history. If many people—or no one at all—died when the specific stone was transported, or a famous sailor brought it in, the value of the rai stone increases by reason of its anecdotal heft. Rai stones were, and still are, used in rare important social transactions, such as marriage, inheritance political deals, sign of an alliance, ransomof the battle dead or, rarely, in exchange for food. Many of them are placed in front of meetinghouses or along pathways. The physical location of the stone may not matter—though the ownership of a particular stone changes, the stone itself is rarely moved due to its weight and risk of damage. The names of previous owners are passed down to the new one.

In one instance, a large rai being transported by canoe and outrigger was accidentally dropped and sank to the sea floor. Although it was never seen again, everyone agreed that the rai must still be there, so it continued to be transacted as genuine currency.

What is important is that ownership of the rai is clear to everyone, not that the rai is physically transferred or even physically accessible to either party in the transfer.

The stones vary widely in size: the largest are 3.6 meters (12 ft) in diameter, 0.5 meters (1.5 ft) thick and weigh 4 metric tons (8,800 lb). The largest rai stone is located on Rumung island, near Riy village.  Smaller rai stones might have a diameter of 7–8 centimetres.