Rai stone Yap Island; post-O'Keefe type

There was no standard size or weight for these, resulting in a great variance of both. The smallest sizes are around 3.5 centimeters, whereas the largest sizes are around 360 centimetres (with the heaviest weighing around 4,000 kilograms). The average size is thought to be around 90 centimetres.

These stones can be classified into two general types: the pre-O'Keefe type and the post-O'Keefe type. The post-O'Keefe type is known by a pronounced central lip and smoother carving (as a result of obtaining better tools), whereas the pre-O'Keefe types are much cruder.

David Sean O'Keefe was an Irish-American captain who made a business by transferring the Yapese to Palau, where the limestone was quarried, and transfering the people and stone back to Yap. Before O'Keefe, when the Yapese would make the journey themselves, the journey was difficult and often resulted in the loss of life, with both the time it took and the life lost affected the value of the stone. But after O'Keefe arrived, the journey and transportation became easier (which made even larger sizes possible to transport); however, this also meant that the post-O'Keefe stones were seen as less valuable than the older ones.

Because some of these stones were so large, when they made it back to Yap, they would be inconvenient to transfer in everyday transactions. Rather than moving these pieces, their ownership was recorded through oral history, with a transaction involving an announcement of the change of ownership.

This system worked so well that, even if a stone was lost (for example: dropped in the sea), everyone agreed it still existed, and those stone could also be used in transactions (source).

The exact dates of production are uncertain; however, there are early accounts that these Rai stones were produced as early as the 1700s. O'Keefe made his business between 1872 and 1901, which would be the dividing line between the pre-O'Keefe type and the post-O'Keefe types. In 1901, after some trade disputes between Spain (who administered the island) and Germany, Germany officially acquired Yap and imposed stricter regulations. As a result of these trade disputes, the Rai stones ceased production.

While these Rai stones are no longer produced today, they are a valued symbol amongst the Yapese and are sometimes still exchanged in traditional ways.

For a more detailed history and analysis of these Yapese Rai stones (including the specifications of over 100 pieces in museums, including pictures), please read The Stone Money of Yap: A Numismatic Survey by Cora Lee C. Gillilland.