What is obsidian hydration dating

Although relatively infrequent the use of SIMS on obsidian surface investigations has produced great progress in OHD dating.SIMS in general refers to four instrumental categories according to their operation; static, dynamic, quadrupole, and time-of-flight, TOF.In fact, the saturation layer on the surface forms up to a certain depth depending on factors that include the kinetics of the diffusion mechanism for the water molecules, the specific chemical structure of obsidian, as well as the external conditions affecting diffusion (temperature, relative humidity, and pressure).

The use of Secondary ion mass spectrometry (SIMS) in the measurement of obsidian hydration dating was introduced by two independent research teams in 2002. It has also been applied in South America, the Middle East, the Pacific Islands, including New Zealand and Mediterranean Basin.

To measure the hydration band, a small slice of material is typically cut from an artifact.

Over time, water slowly diffuses into the artifact forming a narrow "band," "rim," or "rind" that can be seen and measured with many different techniques such as a high-power microscope with 40-80 power magnification b) depth profiling with SIMS (secondary ion mass spectrometry), and IR-PAS (infra red photoacoustic spectroscopy).

as a result of radiocarbon dating of associated materials).

This sample is ground down to about 30 micrometers thick and mounted on a petrographic slide.

The hydration rind is then measured under a high-power microscope outfitted with some method for measuring distance, typically in tenths of micrometers.

In case of measuring the hydration rim using the depth profiling ability of the secondary ion mass spectrometry technique, the sample is mounted on a holder without any preparation or cutting. There are two general SIMS modes: static mode and dynamic mode, depending on the primary ion current density, and three different types of mass spectrometers: magnetic sector, quadrupole and time-of-flight (TOF).

Any mass-spectrometer can work in static mode (very low ion current, a top mono-atomic layer analysis), and dynamic mode (a high ion current density, in-depth analysis).

In essence it is a technique with a large resolution on a plethora of chemical elements and molecular structures in an essentially non destructive manner.

Tags: , ,