Rai stones

A rai stone (Yapese: raay), or fei stone, is one of many large artifacts that were manufactured and treasured by the native inhabitants of the Yap islands in Micronesia. They are also known as Yapese stone money or similar names.

The typical rai stone is carved out of crystalline limestone and shaped like a disk with a hole in the center. The smallest may be 3.5 centimetres (1.4 in) in diameter. The largest extant stone is located on Rumung island, near the Riy village; it is 3.6 metres (12 ft) in diameter and 50 centimetres (20 in) thick, and weighs 4,000 kilograms (8,800 lb).

Rai stones were quarried on several of the Micronesian islands, mainly Palau, but briefly on Guam as well. The practice stopped in the early 20th century. Today around 6,000 large rai stones are on the island, and several can be seen in museums worldwide.

The stones were highly valued by the Yapese and used for important ceremonial gifts. The ownership of a large stone, which would be too difficult to move, was established by its history as recorded in oral tradition rather than by its location. Appending a transfer to the oral history of the stone thus effected a change of ownership.

Some modern economists have viewed Rai stones as a form of money, and the stones are often used as a demonstration of the fact that the value of some forms of money can be assigned purely through a shared belief in said value.