The island of Yap in the Pacific Ocean used varying sized stones as money, of which the largest weighing several tons were the most valuable. The stones had been brought by sea from the Island of Palau 210km away. [...] The Yapese valued them because large stones were quite difficult to steal and were in relatively short supply. However, in 1874, an enterprising Irishman named David O'Keefe hit upon the idea of employing the Yapese to import more “money” in the form of shiploads of large stones, also from Palau. O'Keefe then traded these stones with the Yapese for other commodities such as sea cucumbers and copra. Over time, the Yapese brought thousands of new stones to the island, debasing the value of the old ones. Today they are almost worthless, except as a tourist curiosity.
From Wikipedia. It's given as an instance of hyperinflation.