Mmbul, Gaw, Fe' or Rai, Yar, and Reng

Two Chiefs of Yap Island Western Caroline Islands
with three perforated stones

Rai, or stone money, are large, circular stone disks carved out of limestone formed from aragonite and calcite crystals. Rai stones were mined in Palau and transported for use to the island of Yap. They have been used in trade by the locals and are described by some observers as a form of currency.
There are five major types of rai stone monies:Mmbul, Gaw, Fe' or Rai, Yar, and Reng.
The considered value of a specific stone is based on its size and craftsmanship and also on the history of the stone. 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. Rai stones were and still are used in rare, important social transactions such as marriage, inheritance, political deals, sign of an alliance, ransom of the battle dead or, rarely, in exchange for food. Many of them are placed in front of meeting houses or along pathways.
Ownership is transferred without physically relocating the stones.
- See more at: http://www.maritimeheritage.org/ports/gilbertIslands.html#sthash.vEhsXQWS.dpuf

Two Chiefs of Yap Island Western Caroline Islands 
with three perforated stones

Rai, or stone money, are large, circular stone disks carved out of limestone formed from aragonite and calcite crystals. Rai stones were mined in Palau and transported for use to the island of Yap. They have been used in trade by the locals and are described by some observers as a form of currency.
There are five major types of rai stone monies: Mmbul, Gaw, Fe' or Rai, Yar, and Reng.
The considered value of a specific stone is based on its size and craftsmanship and also on the history of the stone. 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. Rai stones were and still are used in rare, important social transactions such as marriage, inheritance, political deals, sign of an alliance, ransom of the battle dead or, rarely, in exchange for food. Many of them are placed in front of meeting houses or along pathways.
Ownership is transferred without physically relocating the stones.

http://www.sil.si.edu/smithsoniancontributions/HistoryTechnology/pdf_hi/SSHT-0023.pdf

Federal Reserve Bank of Cleveland, Island Money, by Michael F. Bryan: 
Consider the case of the Irish American David O’Keefe from Savannah, Georgia, who, after being shipwrecked on Yap in the late nineteenth century, returned to the island with a sailing vessel and proceeded to import a large number of stones in return for a bounty of Yapese copra (coconut meat). The arrival of O’Keefe (and other Western traders) increased the number and size of the stones being brought back to the island, and by one accounting, Yap stones went from being “very rare” in 1840 to being plentiful—more than 13,000 were to be found on the island by 1929. No longer restricted by shell tools and canoes, the largest stones arriving grew from four feet in diameter to the colossal 12-foot stones that are now a part of monetary folklore. Yet the great infusion of stones did not inflate away their value. Since the stones of Captain O’Keefe were obviously more easily obtained, they traded on the island at an appropriately reduced value relative to the older stones gotten at much greater cost. In essence, O’Keefe and other Westerners were bringing in large numbers of “debased” stones that could easily be identified by the Yapese.

The following portion of the history of the stone money is agreed upon.

a. Urun and Tamangiro, from Af Village, in Tamil Munici- pality, went to the Palau Islands and obtained three pieces of stone money. They gave the larger piece to the people of Af Village. By agreement between them, Urun retained one of the smaller ones and Tamangiro the other smaller one. The piece in question in this action is the one retained by Urun in this division.

b. Urun's house burned down and the people of Af Village helped him rebuild it. In payment of this assistance, Urun gave the stone money now in question to the people of Af Village.

c. During a "tarn" celebration given by Af Village, the people of Dechumui Village put on a dance about people going on a trip and, in appreciation for this dance, the people of Af Village gave the stone money in question, among other things, to the people of Dechumur Village and the stone money was removed to Dechumur Village and remained there until about January 15, 1960.

d. Some people from Dechumur Village made a trip to Palau and brought more stone money of various sizes. The piece brought in on this trip by Tamag was the same size as that given by Af Village to Dechumur Village, and this piece brought in by Tamag was given to Af Village and the piece now in question given to Tamag in exchange for the one he brought in.

e. Tamag gave the piece now in question to his brother Fazagol when the latter was about to build a house. Fazagol gave this stone money to Puguu in payment for some tin roofing for the house.

f.    On or about January 15, 1960, the defendant Pong, with a group of men gathered by him, removed the stone money in question from Dechumur Village over the protests of the plaintiff Choo who was present during part of the removal, protested that the stone money belonged to him, and told them not to remove it. Later, on Pong's authorization, the stone money was shipped to the Money Museum of the National Bank of Detroit, Michigan, in accordance with the agreement of sale with Pong under which he received $125.00 for the stone money.