Perhaps the most well-known obsidian source in the Greater Yellowstone Area is Obsidian Cliff. There are 19 known obsidian sources used by prehistoric peoples in the Yellowstone region spread out to the south, southwest, west, and northwest, offering choice and opportunity (Park 2011). Through time, several Native American cultures had knowledge of and access to different obsidian sources in the GYE. The trace elements Zinc (Zn) and Gallium (Ga) are also recorded but not considered diagnostic of distinct chemical groups because they “don’t usually vary significantly across obsidian sources ” (Hughes 2007). These diagnostic elements are, therefore, most useful in distinguishing between different geochemical sources. These elements are considered “diagnostic,” signifying these trace elements are well-measured by EDXRF and show high variability between sources, while maintaining low intra-source variability (Hughes 2007).

Richard Hughes, personal communication 2008). When determining the geochemical “source” of an obsidian artifact, certain trace elements are assigned more analytical weight based on findings elements Rubidium (Rb), Strontium (Sr), Yttrium (Y), and Zirconium (Zr) show the most consistent inter-source variability for the region (Dr.

Intra-source variability in obsidian typically falls into a predictable range for those sources in the Yellowstone area. Instrumental trace element analysis of obsidian can be performed and results obtained through energy dispersive x-ray fluorescence (EDXRF), which is a relatively inexpensive, non-destructive, and highly accurate technique for mapping a source’s fingerprint. Obsidian, on the other hand, is an ideal tool stone for determining source affinity to a degree that is archeologically applicable.

The process is expensive, and the results are not always of a nature useful to archeological research questions. However, cryptocrystalline materials have a high degree of intra-source variability. The source affinity of cherts and other cryptocrystalline materials (locally available and frequently used tool stones in Yellowstone) can also be determined at the trace elemental level. Thus, tools made of obsidian can be traced back to their source using this fingerprint, providing insight to archeological analysis of trade and travel routes and potentially even cultural significance for tool stone collection areas. Obsidian is also “prized” by archeologists, for one key reason: this material and other rhyolites can be analyzed for their chemical composition, which provides a unique signature or “fingerprint” for each source. In addition, some of the places where obsidian was collected or quarried were considered culturally significant to a number of tribes who historically inhabited this area, perhaps further adding to the preference for obsidian as a tool stone material (Park 2010). Obsidian was also abundantly available in the GYE, which was convenient for the highly mobile hunter-gatherers who called this land home prior to the arrival of non-Native people. This is the reason for obsidian’s conchoidal fracture pattern and allows for easy flaking and sharp edges (up to 10 times sharper than surgical steel), qualities that make it an excellent tool stone. As a glass, the atomic structure of obsidian is “disordered,” which means it has no “preferred direction of fracture” (Shackley 2005). It was generally the most popular tool stone material used by the ancestors of Native Americans in the Greater Yellowstone Ecosystem (GYE) and was prized as a tool stone material for practical (and potentially cultural) reasons. Obsidian is a volcanic glass formed when magma is extruded from the earth’s crust and cools very rapidly, with little moisture content or crystalline inclusions. Obsidian: The MVP of Yellowstone’s “Stones” Watson, courtesy National Park Service, Yellowstone National Park. Obsidian from this source is found in Hopewellian burial mounts in the Ohio River Valley.

Obsidian stones