Yap is known for its stone money, known as Rai: large doughnut-shaped, carved disks of (usually) calcite, up to 4 m (12 ft) in diameter (most are much smaller). The smallest can be as little as 3.5 centimetres (1.4 in) in diameter.[4] There are five major types of monies: Mmbul, Gaw, Fe' or Rai, Yar, and Reng, this last being only 0.3 m (1 ft) in diameter. Many of them were brought from other islands, as far as New Guinea, but most came in ancient times from Palau. Their value is based on both the stone's size and its history. Historically the Yapese valued the disks because the material looks like quartz, and these were the shiniest objects around. Eventually the stones became legal tender and were even mandatory in some payments.[5]