The Wikipedia article on Yapese rai stones is fascinating:
"Although the ownership of a particular stone might change, the stone itself is rarely moved due to its weight and risk of damage. The names of previous owners are passed down to the new one. In one instance, a large rai being transported by canoe and outrigger was accidentally dropped and sank to the sea floor. Although it was never seen again, everyone agreed that the rai must still be there, so it continued to be transacted as genuine currency. What is important is that ownership of the rai is clear to everyone, not that the rai is physically transferred or even physically accessible to either party in the transfer. In this, the rai stone monetary system can be thought as an early example of a distributed ledger, similar to those used in modern days blockchain technology.
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In 1871, the Irish-American David Dean O'Keefe was shipwrecked near Yap and was helped by the natives. Later, he assisted the Yapese in acquiring rai and in return received copra and trepang, which were valuable exports in the Far East. O'Keefe provided the Yapese with iron tools. As a result, a form of inflation set in and rai stones acquired with his help were less valuable than more ancient ones."
