Obsidian is a kind of volcanic glass and was highly prized for making certain kinds of stone tools. Obsidian forms at places of relatively small outflows of magma, or liquid rock. Small flows can cool quickly, which allows the formation of a glassy crystalline structure ideal for stone tool manufacture. Small flows also represent a small sample of well-mixed magma, and thus each little patch of obsidian may share a very distinctive chemical signature. This signature, usually identified by trace elements such as Strontium, Zirconium, Yttrium and Rubidium, then allows for the chemical fingerprinting of each source. Any obsidian artifact found, whether at a source or not, can also be “fingerprinted” and then compared to a catalogue of known obsidian ources. Since the artifacts don’t move around on their own but only through the agency of humans, the distribution of obsidian artifacts is a proxy measure for the movement and interaction of people. When you have hundreds or thousands of such artifacts and a large database of known sources, then you can start to see large scale, long-term social interaction emerge from the silent archaeological record. Most obsidian isn’t visually distinctive enough to sort out by eye alone, so these geochemical methods are essential.
So far, so Archaeology 101. I was really happy to find that Oregon’s Northwest Research Obsidian Studies Laboratory has a web site not which not only solicits business, but is a highly educational and informative site about many aspects of obsidian analysis, with a focus on the Northwest. Continue reading