The Waluta Yap

The exchange rate of stone money

...the coins were made of aragonite, a material that is not available on Yap, but had to be transported from the island of Palau, approximately 400 km away. The transportation of the material would have taken at least five days over the rough Pacific, and often took the lives of men. The value of the coin depended (and still does) on its diameter, but the number of sailors that were killed in its transportation also have an effect on the value. The more casualties, the more the coin was worth. There is certain logic in this.

(Thanks, Kirby!)