The island of Yap is notable for its "stone money" (Rai stones), large disks usually of calcite, up to  in diameter, with a hole in the middle. The islanders, aware of the owner of a piece, do not necessarily move them when ownership changes. There are five major types: ''Mmbul'', ''Gaw'', ''Ray'', ''Yar'', and ''Reng'', the last being only  in diameter. Their value is based on both size and history, many of them having been brought from other islands, as far as New Guinea, but most coming in ancient times from Palau. Approximately 6,500 of them are scattered around the island.