OBSIDIAN DENSITY, CONNATE WATER AND HYDRATION DATING

Abstract

The search by many authors for the chemical components most influential in determining hydration rates, for obsidian dating purposes, has had mixed results. Recently it has been demonstrated that hydration dating is more reliable when individual artifacts are assayed for their compositional or connate water content, rather than relying on a single source specific chemical compositional determination which may overlook the formational water variations between different parts of an obsidian flow. Water measurement may be difficult to achieve for every dateable artifact using the currently preferred system of infrared spectroscopy; small sample size and lack of transparency can significantly reduce the quality of the measurement. The relationship between obsidian connate water and density is presented to show that simple density measurement can in many cases be an alternative to infrared spectroscopy. Results from the analysis of 31 obsidians ranging from North America to the southwest Pacific show that useful estimations of obsidian connate water can be achieved by density measurement. An important finding is the marked difference between the potential hydration rates of 'dry' higher density obsidians of the southwest Pacific compared with 'wet' lower density specimens from North America.