How does obsidian hydration dating work?
Obsidian, which is a glassy volcanic rock, absorbs moisture from the atmosphere to form a thin hydration rind in the outer layer of the obsidian and this layer slowly increases in thickness over time. The hydration rind on artifacts is not visible to the naked eye but can be measured from a small slice, or thin section, cut from the edge of an obsidian artifact and mounted on a microscope slide. Through a microscope, the hydration rind is measured in microns (thousandths of a centimeter or four hundred-thousandths of an inch). Once the thickness of the rind is known, formulas for calculating the time it took for the rind to form can be applied to estimate its age. Obsidian hydration dating is less precise and less reliable than radiocarbon dating but provides a technique for directly dating artifacts.
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