Obsidian, natural glass formed during volcanic eruptions, was an important raw material in prehistory worldwide. Obsidian was prized for tool making for a number of reasons, including its workability, sharpness, and visual appeal. Consequently, prehistoric peoples went to great lengths to obtain obsidian, often from very distant sources. For archaeologists, obsidian is a powerful tool for understanding prehistoric economy and interaction, because individual obsidian outcrops are usually spatially discrete and chemically distinct from one another. During the 1960s, archaeologists began to utilize techniques to geochemically characterize obsidian sources and archaeological artifacts. Examination of regional patterning in obsidian procurement can provide valuable information about ancient trade routes and social connections.
Obsidian Survey at Wallace Tank, Arizona (left) and scatter of obsidian nodules at Government Mountain, Arizona (right). Photos courtesy of James Meierhoff.
Obsidian is restricted to volcanic regions, and in the United States, obsidian outcrops are widely distributed in the Mountain West, Southwest, California, Oregon, and Washington State. Many of these sources are represented among Native American artifacts housed in the Museum's North American collections. The Field Museum Anthropology Department recently began building up a collection of obsidian source samples from the American West for use in identifying the sources from which these artifacts originated. During survey work in the Fall of 2010, Field Museum researchers visited sources in northern Arizona and New Mexico. Additional source samples, provided by archaeologists at Idaho State University, have been acquired from important sources in Oregon, Idaho, and Wyoming. At present, more than 30 chemically distinct sources are represented in our North American obsidian collections.
Photo: Obsidian from Government Mountain, Northern Arizona, courtesy of James Meierhoff.