Obsidian Hydration Research Articles

Chemical characterization and hydration rate development for New Mexican obsidian sources

AbstractThe obsidian hydration dating of prehistoric sites requires that each type of natural glass be identified on the basis of its elemental constituents in order that the appropriate hydration rate constants may be applied. In New Mexico, obsidian occurs in the form of in situ flows and as secondarily deposited detrital material in the sediments of ancestral watercourses. the chemical analysis of 153 geological and archaeological samples from both contexts has resulted in the identification of nine major obsidian sources. the hydration rates for New Mexican obsidians developed by different researchers are compared and evaluated in light of current knowledge on glass‐water interaction. It is argued that a hydration rate developed in silica saturated solution or at 100% relative humidity are the preferred conditions for laboratory hydration rate development.

Obsidian Hydration Dating of Tecep Phase Occupation at Nohmul, Belize

In spite of deranging factors that have retarded full acceptance, the obsidian hydration dating method has potential for archaeology. Its application to 16 obsidian samples from a Tecep phase burial (A.D. 800-1100+) at the Maya site of Nohmul, Belize, suggests late persistence of occupation and allows for resolution of a stratigraphic problem.

Obsidian Hydration Rate Development

AbstractSince the seminal work of Friedman and Smith [1] obsidian hydration dating (OHD) has undergone several important stages of development and refinement. This paper will summarize the history of research and developments as to elucidate some areas for future research.Archaeologists have taken a pragmatic and empirical approach towards OHD and hydration rate determination. They would like OHD to become an absolute chronometric technique. Geochemists and material scientists have sought to understand the hydration process from an environmental, chemical and thermodynamic perspective. As suggested by the literature, obsidian hydration appears to be a diffusion, reaction and dissolution process dependent on the chemical and thermal history of the hydration environment. Although there appear to be certain central tendencies, however, there are discrepancies between empirical archaeologically-derived data and theoretical models.California offers a rich data base for synthesis and testing of hydration models. There are over 25 natural obsidian sources many of whose chemical and physical properties have been measured by Ericson [2]. Obsidians have been distributed aboriginally as artifacts into diverse environments. Intensive excavations, underwritten by extensive land development, have contributed to development of a number of source-specific hydration rates for single sources. Reanalysis of the California data warrants future examination to advance our understanding of obsidian hydration dating on a world wide basis.

Obsidian Hydration Rate Development

ABSTRACTSince the seminal work of Friedman and Smith [1] obsidian hydration dating (OHD) has undergone several important stages of development and refinement. This paper will summarize the history of research and developments as to elucidate some areas for future research.Archaeologists have taken a pragmatic and empirical approach towards OHD and hydration rate determination. They would like OHD to become an absolute chronometric technique. Geochemists and material scientists have sought to understand the hydration process from an environmental, chemical and thermodynamic perspective. As suggested by the literature, obsidian hydration appears to be a diffusion, reaction and dissolution process dependent on the chemical and thermal history of the hydration environment. Although there appear to be certain central tendencies, however, there are discrepancies between empirical archaeologically-derived data and theoretical models.California offers a rich data base for synthesis and testing of hydration models. There are over 25 natural obsidian sources many of whose chemical and physical properties have been measured by Ericson [2]. Obsidians have been distributed aboriginally as artifacts into diverse environments. Intensive excavations, underwritten by extensive land development, have contributed to development of a number of source-specific hydration rates for single sources. Reanalysis of the California data warrants future examination to advance our understanding of obsidian hydration dating on a world wide basis.

Obsidian Hydration Dating - Field, Laboratory, and Modeling Results

AbstractHydration rind thicknesses found on obsidian artifacts provide one means of estimating the age of an archaeological site. The model used in the method usually assumes a diffusion-controlled reaction of the glass with water. However, results using this model are not always in agreement with other dating methods. Observations of secondary mineral formation on glasses in contact with water vapor suggests that other rate-controlling mechanisms may be operative. In this paper, we apply the glass dissolution code GLASSOL, coupled with the geochemical code PHREEQE to model the reaction of Glass Mountain obsidian in water. The results show the importance of accounting for the effects of solution chemistry on the time-dependence of the hydration reaction.

Obsidian Hydration Dating - Field, Laboratory, and Modeling Results

ABSTRACTHydration rind thicknesses found on obsidian artifacts provide one means of estimating the age of an archaeological site. The model used in the method usually assumes a diffusion-controlled reaction of the glass with water. However, results using this model are not always in agreement with other dating methods. Observations of secondary mineral formation on glasses in contact with water vapor suggests that other rate-controlling mechanisms may be operative. In this paper, we apply the glass dissolution code GLASSOL, coupled with the geochemical code PHREEQE to model the reaction of Glass Mountain obsidian in water. The results show the importance of accounting for the effects of solution chemistry on the time-dependence of the hydration reaction.

The Coso volcanic field reexamined: Implications for obsidian sourcing and hydration dating research

AbstractObsidian from the Coso locality, Inyo County, California, has long been regarded by archaeologists as a single “source.” However, studies by the U.S. Geological Survey have provided evidence of geochemical variability among flows within the volcanic field. to determine whether these geochemical distinctions could be applied productively to archaeological research, nondestructive x‐ray fluorescence analyses were conducted on samples recently collected from 15 obsidian‐bearing loci. the results of this research show that geochemically distinct varieties of artifact‐quality obsidian can be recognized within the Coso volcanic field, and subsequent nondestructive x‐ray fluorescence analyses of artifacts from two nearby archaeological sites document that different geochemical varieties of obsidian were used prehistorically to manufacture tools. Implications of these results for studies of prehistoric exchange and obsidian hydration dating are discussed.

Glass Hydration Mechanisms with Application to Obsidian Hydration Dating

AbstractChemical analysis of typical obsidians place them with a group of silica- and alumina-rich glasses constructed of a three dimensional framework of silica and alumina tetrahedra with nearly all tetrahedra sharing corners. Raman and infrared spectra of unweathered obsidians confirm the high degree of polymerization as well as some additional structural disorder. Analysis of dissolution rates of various glasses shows obsidian to be among the most stable, comparable to the most durable synthetic glasses. Surface layers on glasses can be chemically characterized by depth-profiling techniques such as SIMS and SIPS that give depth-concentration profiles for individual elements. Hydration rinds on glasses can be structurally characterized by infrared spectroscopy which shows both hydration and re-polymerization as the rinds age. Because obsidians are already completely polymerized glasses, their hydration rinds are mainly a result of hydrolysis and alkali exchange.

Glass Hydration Mechanisms with Application to Obsidian Hydration Dating

ABSTRACTChemical analysis of typical obsidians place them with a group of silica- and alumina-rich glasses constructed of a three dimensional framework of silica and alumina tetrahedra with nearly all tetrahedra sharing corners. Raman and infrared spectra of unweathered obsidians confirm the high degree of polymerization as well as some additional structural disorder. Analysis of dissolution rates of various glasses shows obsidian to be among the most stable, comparable to the most durable synthetic glasses. Surface layers on glasses can be chemically characterized by depth-profiling techniques such as SIMS and SIPS that give depth-concentration profiles for individual elements. Hydration rinds on glasses can be structurally characterized by infrared spectroscopy which shows both hydration and re-polymerization as the rinds age. Because obsidians are already completely polymerized glasses, their hydration rinds are mainly a result of hydrolysis and alkali exchange.

Induced Obsidian Hydration Experiments: An Investigation in Relative Dating

AbstractInduced obsidian hydration experiments have been conducted over the last six months at Sonoma State University. Our initial focus has been to assess the influence of experimental conditions on hydration development within a thermally controlled pressure reaction vessel. Although an ultimate goal is to calculate source-specific rates for local obsidians, given current uncertainties regarding the ability to reliably express hydration widths as calendar years, a more immediate goal is to develop a means to compare hydration rim measurements of samples from one obsidian source relative to another so that archaeological assemblages containing obsidians from two or more sources can be placed into a time series. Induced hydration experiments are expected to provide data that illustrate the relationship between hydration measurements of different obsidians with temporal equivalency. Results and implications of initial experiments are discussed.

Household Remains of the Humblest Maya

AbstractEight small rural sites with 27 associated structures have been intensively excavated in the Copan Valley Honduras, as part of a larger program of settlement analysis. These excavations, which include peripheral spaces around structures, provide what is currently our best sample of rural domestic household remains of Maya “commoners” or “producers,” who have been largely ignored by a tradition of archaeological research focused on major centers. Data derived from this research have both methodological and substantive implications for understanding prehistoric Maya settlement systems at Copan and elsewhere. An ambitious program of obsidian hydration analysis not only effectively dates these particular sites, but indicates that our concepts concerning demographic and political processes associated with the Maya “collapse” at Copan must be radically changed.

Induced Obsidian Hydration Experiments: An Investigation in Relative Dating

ABSTRACTInduced obsidian hydration experiments have been conducted over the last six months at Sonoma State University. Our initial focus has been to assess the influence of experimental conditions on hydration development within a thermally controlled pressure reaction vessel. Although an ultimate goal is to calculate source-specific rates for local obsidians, given current uncertainties regarding the ability to reliably express hydration widths as calendar years, a more immediate goal is to develop a means to compare hydration rim measurements of samples from one obsidian source relative to another so that archaeological assemblages containing obsidians from two or more sources can be placed into a time series. Induced hydration experiments are expected to provide data that illustrate the relationship between hydration measurements of different obsidians with temporal equivalency. Results and implications of initial experiments are discussed.

Comment on “Tomato Springs: The Identification of a Jasper Trade and Production Center in Southern California”

Marie Cottrell's recent (1985) proposal that prehistoric long distance exchange of jasper occurred between the California coast and inland deserts is most unlikely in light of the presence of abundant secondary siliceous sediment sources (including jasper) along the nearby southern California coast. The obsidian hydration based site chronology at Tomato Springs, founded on non-source provenienced obsidian, is equally problematic. A number of other lesser potential fallacies serve to undermine the assumption of long distance transport of a raw material that was available locally.

A Twin-Bladed Diamond Saw for Obsidian Hydration Labs

A Twin-Bladed Diamond Saw for Obsidian Hydration Labs

Obsidian Hydration Dating of the Desert Culture on the Coconino Plateau

Obsidian hydration dating has been used in past attempts to date preceramic Desert culture occupation of the Coconino Plateau just south of Grand Canyon. The use of this technique is critically examined, and it is argued that, due to inappropriate application of the technique, neither the cultural phases proposed for the area nor the attributes said to characterize each phase are valid. The current status of dating the Coconino Plateau Desert culture is reviewed, and suggestions are made regarding acceptable application of obsidian hydration dating as a means of establishing a preceramic chronology for the area.

Obsidian hydration dating

The accurate dating of uncovered artifacts is of fundamental importance in archaeology. Since the war radiocarbon has proved immensely valuable for specimens with an organic content. For sites producing obsidian or other natural glasses this has been rivalled during the past decade by obsidian hydration dating. Although this demands careful attention to the conditions on particular sites, it is capable of yielding accurate dates in the range 1 000 000 to 200 BP.

Obsidian Hydration Dating in the Undergraduate Curriculum

Hydration rate measurements in obsidian artifacts have been used for dating purposes for a quarter of a century. The technique reveals the dates of archaeologic, anthropologic and geologic events during the last several thousand years of Earth history. A simple measurement of the depth of water penetration from the surface of the obsidian may give valuable information to the student of archaeology, anthropology and geology, with a minimum of effort, time, and expense. The theory of the method and one or more laboratory exercises can be easily introduced in a variety of undergraduate curricula. To encourage this, the article gives an overview of obsidian hydration dating for the instructor by presenting the principles, procedures, applications and limitations of the method.

Evaluating the Occupational History of Lithic Scatters: Analysis of Obsidian Hydration Measurements

Surface lithic scatters often pose problems for archaeological interpretation because temporally different occupations cannot be distinguished stratigraphically. When composed primarily of obsidian, however, the occupational history of a lithic scatter can be assessed upon analysis of its hydration measurements. A sample of hydration measurements drawn from the scatter are visually displayed using box and whisker plots, and analyzed using two inferential procedures (the W test for normality and Chauvenet's criterion) designed to test whether or not the sample is drawn from a single population. Application of the inferential procedures relies on assumptions about the hydration phenomena. This analysis provides a visual and objective means to decide whether a population of obsidian artifacts was created over a short span of time, or during more than one discrete occupational episode.

Easter Island Subsistence.

Research conducted on Easter Island habitation sites provides evidence concerning the local prehistoric and protohistoric subsistence base. Quantified data on faunal remains in midden are evaluated for reliability as indicators of the relative importance of domesticates and marine food resources in island subsistence and for population size estimate. A review of subsistence oriented research in the Pacific includes discussions of initial attempts to identify subsistence bases qualitatively, later quantifications of faunal and other subsistence information, a consideration of the development of economic prehistory, and finally, a summary of insights derived through ethno-archaeological approaches. A review of previous research on Easter Island provides very little quantified subsistence information. Quantifiable faunal data on three major food remains, fish, chicken, and shellfish, are available from my research. Obsidian hydration measurements allow short-term dating; several sites overlap timewise from about A.D. 1200 to the present. Identification of fish classes (genera) from skeletal remains is hindered by an incomplete comparative collection, but it is possible to recognize the fishing methods and technology used. The data provides evidence for the limited importance of offshore (pelagic) fishing and a great reliance on chicken as a protein source. Shellfish were never of great significance in diets primarily because of their small size. A preliminary definition of the subsistence strategies developed by the Easter Islanders is possible. This paper is suggested as a contribution toward attaining reliable population estimates, for understanding the relationships between levels of technology and subsistence patterns and for recognizing the relative importance of domesticates versus collected food resources on Easter Island and on Pacific islands in general.

A tritium-exchange method for obsidian hydration shell measurement

A new radiochemical method for measuring the amount of water in the hydrated layer on the surface of obsidians exchanges tritiated water with the water in the layer (20 μl of 5 Ci ml −1 at 90°C for 10 days) and then back-exchanges it (in 150 ml of water at 35°C for ∼ 200 hr.). The activity of the back-exchange water ( F) is monitored by liquid scintillation counting of aliquots extracted at known time intervals ( t). The activity so measured is then related to the thickness of the hydration rim. A sheet diffusion model shows that the thickness of the hydration shell ( l) is inversely proportional to the slope of the F vs. t 1 2 plot. Comparison of l-values so obtained between obsidians, whose age ( x) is inferred from archaeological occupation layers containing radiocarbon-dated wood and charcoal, suggests a relationship between l and x. Implications for New Zealand prehistory are briefly considered. The technique, which is non-destructive, appears particularly applicable to young glasses where the development of hydrated layers may be inadequate for accurate optical measurement.