Rai stones
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).
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.
[12] Earlier reports incorrectly state that the material is aragonite, the most common mineral in coral and sea shells and in rocks derived thereof.
[13][14][9] The stone occurs in Palau as deposits slowly formed on the walls of some caves by percolating rainwater (speleothems, specifically flowstones).
Tectonic activity millions of years ago lifted limestone deposits out of the sea, eroded by rainwater, forming a typical cave-riled karst geology.
However, there are small veins of marble, a crystalline calcite rocks of metamorphic origin, that has a sparkling appearance similar to that of the Palau flowstones.
It has been conjectured that the Yapese originally came to value crystalline calcite from these sources before discovering the much more abundant deposits in the Palau caves.
[14] Archaeologists have identified quarries used by the Yapese in a relatively small region of Palau, spanning the southern end of Babeldaob and the northern part of Koror.
A large stone (3.5 m diameter, 20 cm thick) that apparently broke while being removed from the quarry at Metuker ra Bisech was abandoned on the spot.
Expeditions to Palau, consisting of tens of young men authorized or commanded by a village chief, would last up to several years and could result in the death of members at the quarries or during the sea voyage.
According to some accounts, on their return, the largest stones and 2/5 of the smaller ones were handed over to the chief, and the men were rewarded with baskets of taro.
Eventually the Palau natives gave the Yapese permission to quarry, in exchange for heavy labor and a few other items they brought from Yap.
The rough work appears to have been done with pickaxes or adzes, with blades 1 to 3 cm wide, made of stone or of the shell of large clams such as Tridacna.
[13] (While the clam shells and coral are made of calcium carbonate too, they consist of the aragonite form, which is harder than the stone's calcite (3.5–4.0 and 3.0 in the Mohs hardness scale, respectively).
Since the raft was slow and poorly steerable, it was usually let loose in advance to be carried towards Yap by sea currents, while the men left some time later in canoes, on its pursuit.
[3]}[23] It is reported that the stones were transported on land by inserting a log or bamboo through the hole, which was carried on the shoulders of several men.
His commercial agent Alfred Tetens reported in his memoirs that, in 1865, he transported ten Yapese from Palau to Yap, who were carrying 20 large blocks and many smaller ones, a few cm in diameter, to be used as currency.
[3] Contact with Europeans in the 19th century first provided the Yapese at Palau with iron tools, that made the cutting and shaping of the stones much easier.
Later, he assisted the Yapese in acquiring rai stones and in return received copra and trepang, which were valuable exports in the Far East.
Demands by the government of France for such payment from the United States in 1932 contributed to a nationwide bank panic, proving that industrialized countries could fall under the sway of economic rituals as surely as the Yap islanders.
[8] A 2022 paper by Jo Lindsay Walton, a science fiction author and research fellow at the University of Sussex, claims inconsistencies, errors and omissions in many Western economic accounts of stone money, including Friedman's.
