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Trace Element Analysis of Fused Shale

Abstract Natural glass (obsidian) and fused shale, a glassy metamorphic rock from Santa Barbara and Ventura counties, can be visually similar. In addition to macroscopic resemblance, fused shale and obsidian from Obsidian Butte (Imperial County) share a Rb/Sr/Zr trace element signature that may have led to misidentifications in previous sourcing research. Data from the Playa Vista Archaeological and Historical Project show that fused shale has been misidentified as obsidian, prompting an evaluation of the significance of misidentifications and the degree to which they may impact resource procurement models and archaeological reconstructions of the importance of Obsidian Butte glass in Late Prehistoric coastal southern California.