Discovery Of Ancient Obsidian Quarry Helps Define Prehistoric Andean Trade Networks

April 03, 1997

MADISON - The discovery of an ancient quarry high in the Peruvian Andes, where prehistoric peoples mined and knapped volcanic glass, is providing the first hard evidence that long-distance trade was taking place in the Americas as far back as 2,500 B.C.

Volcanic glass or obsidian was "the material of choice for stone knives, lance and arrow points, and other tools throughout the prehistoric world," according to Sarah Osgood Brooks, a University of Wisconsin-Madison geographer who found the quarry and reported it this week in the April 3 edition of the scientific journal Nature.

The quarry, discovered on the flank of an extinct volcano in Peru's Colca Valley by Brooks and a Peruvian guide, Pedro Huaracha, has been sought for decades by scientists. It is of interest to archeologists because its obsidian, chipped into tools of all sorts, has been found over much of the south-central Andes of Peru and Bolivia.

Since obsidian deposits are rare, and because each deposit has its own distinctive chemical signature, tools made from obsidian leave an indelible trail, illuminating trade networks that existed for thousands of years before the first Europeans set foot in the New World.

"Obsidian comes from volcanoes, but it is the rare volcano that makes it," said Brooks, a doctoral student. "Each obsidian source is compositionally homogenous and distinct from all other obsidian sources. Because each source has a distinctive chemical signature, an artifact can be linked with certainty to a source through chemical analysis."

Chemical analysis of samples from the newly discovered quarry, and analysis of obsidian artifacts found as far as 186 miles away, was conducted by Michael D. Glascock of the University of Missouri's Research Reactor Center. Additional artifacts were contributed by Martín Giesso, an anthropologist from the University of Chicago.

Nearly 75 percent of the artifacts submitted for analysis were identified as coming from the quarry, named the Cotallalli Obsidian Quarry. That so much obsidian was coming from a single source is evidence of the richness of the deposit and, said Brooks, of a well-established and organized network of prehistoric trade.

The quarry, she said, is as large as two football fields and was probably worked for thousands of years by people who chipped fractured chunks of obsidian into transportable blanks and preforms. The ground at the quarry is covered with fist-sized fragments, the majority worked to one degree or another.

"Nearly every single piece appeared to have been worked in some fashion," she said.

Brooks undertook the search for the quarry after finding an abundance of obsidian artifacts in an archeological survey of the area in 1991. She was led to the sight by a native Peruvian who recalled seeing an area covered with obsidian fragments while tracking a wounded deer as a teenager years ago.

The discovery of the quarry is of significant archeological value because scientists can easily read the chemical signatures of obsidian artifacts. If the source of the obsidian used to make an artifact is known, it helps scientists retrace ancient trade routes that were never recorded on any map and that were lost to history when the trade died out after European settlement.

Some of the obsidian artifacts found in the Colca Valley were worked more than 12,000 years ago. It was not always traded, however, and long-distance trade of Cotallalli obsidian can only be reliably traced back as far as 2,500 B.C. However, Brooks said subsequent research may be able to push trade into even the more distant past. She plans to return to the site in 1998 to continue her studies.

Artifacts made from Colca Valley obsidian have been found at archeological sites as distant as Lake Titicaca, 125 miles from the quarry, and at Tiwanaku, 186 mountainous miles away, and the seat of the pre-Inca Tiwanaku empire.

Obsidian from the quarry, said Brooks, may have been especially prized for its translucent nature, giving it aesthetic value beyond its use as a cutting tool.

Obsidian can be worked into some of the sharpest cutting tools known and, until the advent of laser surgery, was used for removing cataracts and performing other delicate surgical tasks, easily outperforming surgical steel.
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- Terry Devitt (608) 262-8282, trdevitt@facstaff.wisc.edu

University of Wisconsin-Madison

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