Archaeometry

In many cultures, obsidian was the preferred material for working into stone tools. When obsidian, which is a volcanic glass, is fractured, the fresh surfaces absorb water. The thickness of the water-absorbing edge, or rind, increases with time. Measurement of the rind with powerful microscopes thus yields a dimension that can be correlated with the age of the tool.

Although this technique has been widely used in California and the Great Basin, it remains a relatively inaccurate technique when used alone to date artifacts.