Abstract
A revised hydration rate for obsidian from the central Arizona Government Mountain-Sitgreaves Peak source area is presented. Data obtained since 1975 suggest that the hydration characteristics of obsidian from 1 to 6,000 years B.P. can best be predicted using a simple squared diffusion model. This new rate improves the accuracy of previously reported rates and, consequently, will increase the usefulness of obsidian hydration dating throughout central and northern Arizona.