MARBLE AS A POTENTIAL LOCAL SOURCE FOR YAPESE STONE MONEY

Yapese stone money are large disk-shaped objects carved out of flowstone precipitates in limestone caves on the Rock Islands of the Republic of Palau and transported as highly prized and valuable items to the island of Yap (Federated States of Micronesia) more than 400 km away in the west-central Pacific. This research focused on calcitic marble from Yap as a possible local source for stone money. Outcrops of marble on Yap are very rare, small and lichen-covered. Two such outcrops within the Miocene Map Formation were examined and a partially carved stone disk was observed at one of the sites. This study considered the geology of Yap marble and its potential significance as a cultural material.

Palau and Yap islands are part of an intra-oceanic island-arc-trench system that separates the Pacific and Philippine plates in the western Pacific. Yap is unusual among intra-oceanic island-arc-trench systems in the area in that it is mainly composed of metamorphic rocks, not typical volcanic rocks. Yap also lacks uplifted middle Tertiary limestone terrains that are common in nearby islands (e.g., Palau and Guam). Such a terrain was never present on Yap or has been completely eroded away. Previous studies interpreted the formation of the Yap volcanic arc-trench system in the early Tertiary by a westward subduction of the Pacific sea floor. Volcanism ended due to blocking of the subduction zone by seamounts and the Caroline Ridge (large mass of thick oceanic crust) causing the deformation, metamorphism, uplift and overthrusting of the sea floor from west of Yap over the former volcanic arc. The Map Fm was interpreted to represent a polymict tectonic breccia that formed along the thrust faults. Blocks of marble within the Map Fm are metamorphosed limestone of either shallow (atoll reefs and lagoons) or deep marine (planktonic ooze) origin.

To our knowledge, this study represents the first documentation of an attempt to carve stone money from marble on Yap, although there are no records of Yapese stone money being made of marble. This could be due to the fact that marble is not abundant on Yap. However, the white color, crystalline texture, and shiny luster of the local marble may have inspired Yapese people to seek similar rock material elsewhere. They found such material and carved most of their stone money from cave flowstones on Palau.