Obsidian hydration dating

Obsidian hydration dating is a geochemical method of determining age in either absolute or relative terms of an artifact made of obsidian.

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Obsidian is the volcanic glass that was sometimes used as raw material for the manufacture of stone tools. When an archeologist has identified the source of the obsidian from which an artifact is made, they may be able to date the artifact using the obsidian hydration technique. This measures the microscopic amount of water absorbed on freshly broken surfaces. The principle behind obsidian hydration dating is simple–the longer the artifact surface has been exposed, the thicker the hydration band will be. Obsidian hydration can indicate an artifact's age if the datable surfaces tested are only those exposed by flintknapping. Obsidian hydration is not effective on surfaces that are uneven due to gradual weathering caused by natural forces.

In order to use obsidian hydration for absolute dating, the conditions that the sample has been exposed to and its origin must be understood or compared to samples of a known age (e.g. as a result of radiocarbon dating of associated materials.

History

Obsidian hydration dating was introduced in 1960 by Irving Friedman and Robert Smith of the U.S. Geological Survey.

See also

• Dating methodology (archaeology)
• Absolute dating
• Relative dating