Obsidian is a natural silica-rich volcanic glass, typically of rhyolitic composition, produced when magma from a deep source erupts onto or near the earth’s surface and rapidly chills against air, water, or some colder rock. Wherever it occurs in the world, obsidian was extensively used in prehistoric and historic times by native peoples to manufacture a wide variety of tools, like projectile points, spears, knives, scrapers and sharp flakes.

Because most obsidian eruptions are highly uniform in chemical composition, it is possible to analyze geological samples to determine the “fingerprint” or trace element profile of each source using a variety of instrumental techniques. Non-destructive energy dispersive x-ray fluorescence (edxrf) analysis is used at GRL to determine the trace and selected minor element composition of geological obsidian samples and archaeological artifacts made from obsidian (see Laboratory Equipment and Methods).