What is "rai stones"

n. (plural of rai stone English)

Rai, or stone money , are large, circular stone disks carved out of limestone formed from aragonite and calcite crystals. Rai stones were quarried on several of the Micronesian islands, mainly Palau, but briefly on Guam as well, and transported for use as money to the island of Yap. They have been used in trade by the Yapese as a form of currency.

While the monetary system of Yap appears to use these giant stones as tokens, in fact it relies on an oral history of ownership. Being too large to move, buying an item with these stones is as easy as saying it no longer belongs to you. As long as the transaction is recorded in the oral history, it will now be owned by the person you passed it on to—no physical movement of the stone is required.