3,300-Year-Old Jade Tool Raises Origin Questions
by AMNH on
The discovery of a small jade tool that was dropped into the waters off an island in the Southwest Pacific about 3,300 years ago is stirring up questions about its origin. The reason for puzzlement: the small green artifact has a chemical composition that is unlike any other described jade, and it was found thousands of miles away from the nearest known geological source.
An international team of archaeologists and geologists from the American Museum of Natural History, the University of Otago (New Zealand), and the University of Papua New Guinea investigate this unusual specimen in a special issue of the European Journal of Mineralogy on jadeitite, the rock that defines one type of jade.
Jade is a general term for two extremely tough rocks—jadeite jade (jadeitite) and nephrite jade, each composed almost entirely from a single mineral. Throughout history, these rocks have been made into tools and ornamental gems that were worn, traded, and treasured. Many nephrite jade sources exist, but the prominent locations are China, New Zealand, Russia, and Canada. Far rarer is jadeite jade, which was used by people living in what is now Central America and Mexico over a span of two millennia prior to the arrival of European colonists.
The artifact, thought to have been used as a wood gouge, was recovered from Emirau Island in the Bismark Archipelago of Papua New Guinea. It was likely dropped from a stilt house into the water below and covered by years of beach sand.
The mineral content and chemical composition of the gouge were analyzed by George Harlow, a curator in the Museum’s Department of Earth and Planetary Sciences, with x-ray microdiffraction—a technique that bounces a small beam of x-rays off the specimen to elucidate the atomic structure of the material—and electron microscopy. Both techniques found the rock to be substantially different from that of other jadeitite samples.
But the even bigger mystery is where this unusual rock came from. Only one jadeite source has been reported with similar chemical properties—a site in Baja California Sur, Mexico. If this were the gouge’s original home, though, it would have had to been transported across the Pacific, a highly improbable scenario for the Neolithic people of the time.
For more information about this work, see the Museum’s press release.