obsidian dating

obsidian dating (obsidian hydration dating) [Te].
A method that is able to determine the age of an obsidian tool in terms of when it was made. When obsidian is chipped a thin layer of hydrated rock slowly builds up on the fresh surface. The thickness of the hydration layer can be measured as the basis for an estimate of how long ago the surface was exposed. The technique can be used back to about 25 000 years ago, but there are always difficulties using the technique because the rate of hydration varies in relation to the chemical composition of the obsidian and the local environment in which it is preserved.