Obsidian Hydration Dating: An Improved Optical Technique for Measuring the Width of the Hydration Rim

Abstract

A simple optical method is described that will enhance the color contrast between the outer birefringent hydration rind and the inner unhydrated core on obsidian thin sections used for hydration dating. The technique utilizes a gypsum nccessory plate. The gypsum plate rotates all incoming light by 550nm causing the black isotropic core of the nhsidian to become transparent first‐order pink and interacting with the transmitted light from the birefringent rind, by either addition or subtraction. to produce a second‐order blue or a first‐order yellow color.

Obsidian hydration dating by infrared spectroscopy: method and calibration

“…Conventional approaches use optical microscopy on polished thin-sections (Eerkens et al, 2008). However, the uncertainty associated with each measurement is about þ/À0.25 mm (Stevenson et al, 1987). A comparison of optical readings with hydrogen profiles collected by secondary ion mass spectrometry (SIMS) (Anovitz et al, 1999;Stevenson et al, 2001Stevenson et al, , 2002 and infrared profiling (Yokoyama et al, 2008) shows that the depth of water diffusion extends well beyond the optically defined diffusion front.…”

Obsidians and Tektites: Natural Analogues for Water Diffusion in Nuclear Waste Glasses

“…At the termination of each experiment, each sample was thin-sectioned and the thickness of the birefringent hydration layer measured, using previously described procedures [7]. An Aus Jena optical microscope with a 40X objective *(Note that the same experiments performed in hydrothermal leach tests involve the simultaneous interaction of molecular water diffusion, ion exchange, etching and secondary mineral precipitation [4][5][6].…”

The Camel Site Obsidian:

“…Pioneering work by Ambrose (1979) and Stevenson et al (1988Stevenson et al ( , 1993Stevenson et al ( , 1998Stevenson et al ( , 2000 established relationships between the rate of hydration, the amount of intrinsic water (probably due to the depolymerizing effect of water ions on the silica matrix), and density. This work (especially Stevenson et al 1993) also determined that the amount of water varies significantly from sample to sample in a single obsidian source, requiring artifact-specific measurements of this variable (density) for the purpose of rate estimation.…”