Created November 12, 2007


“Archaeologists commonly use obsidian hydration analysis to effectively date obsidian artifacts via quantification of moisture uptake measured in hydration rinds that has occurred since artifacts were flaked (see Anovitz et al. 1999; Friedman and Long 1976; Friedman and Smith 1960; Friedman and Trembour 1983).  In addition, geochemical trace element analysis of obsidian artifacts is often used to source the locations from which the raw material was initially quarried (Glascock et al. 1999; Hatch et al. 1990; Hughes 1988; 1994).  While it remains relatively clear that thermal alteration of obsidian does not affect its geochemical composition (Shackley and Dilian 2002); it is quite clear that exposure to heat does negatively affect hydration rinds” (Buenger 2002)

observable morphological change of obsidian  Steffen (2002:163)

  1. BulletMatte Finish: Surface dulling similar to weathered or lusterless patina.

  2. BulletSurface Sheen: metallic-like surface luster, cause uncertain, but may be due to organic carbon buildup and/or bubble formation and shallow microscopic crazing.

  3. BulletFine Crazing: Network of shallow cracks forming closed polygons on fresh fractures and flaked surfaces, likely due to differential thermal expansion/contraction.

  4. BulletDeep Surface Cracking: Shallow crevices formed on artifact surfaces, observed in conjunction with deformation, caused by expansion of surface crazing.

  5. BulletVesiculation: Formation of interconnected bubbles within obsidian specimen due to release of volatiles, specimen metamorphism to a foam-like mass.

  6. BulletFire Fracture (field observation): Rapid thermal fracture of specimen (presumably due to differential thermal stress), may initiate near an inclusion.

“With the exception of vesiculation which occurs at 800°C +, specific temperatures ranges are not provided for each of the associated types of thermal alteration defined above.  However, several of the researchers have observed that appreciable thermal alteration of obsidian occurs at temperature in the 450-550°C range.  Overall, research pertaining to the thermal alteration of obsidian suggests the exposure to heat can significantly affect the morphological integrity of obsidian artifacts as well as the potential to derive obsidian hydration dates from affected specimens. As such the integrity of the archaeological record as it pertains to obsidian artifacts may be significantly affected during prescribe and wildland fires” (Buenger 2002). 

Temperatures at which Obsidian Hydration is affected

approximately 250°C - 300 C (382-572 F) - obsidian hydration bands begin to be altered or diffused

approximately 400°C (752 F) - obsidian hydration bands significantly affected or not visible

         450°C – 800°C (842-1472 F) - fracture lines enhanced

exceeding 700°C (1292 F) - obsidian hydration bands may be completely destroyed (Benson 2002; Deal and McLemore 2002; Green et al. 1997; Findlow and Garrison 1982; Halford and Halford 2002; Mazer et al. 1991; Origer 1996; Ridings 1991; Smith 2002; Solomon 2002; Steffen 2002; Trembour 1990). 

        760°C (1292 F) - Obsidian may melt

As such, diffuse or destroyed hydration rinds render a specimen unsuitable for obsidian hydration analysis.  Thermal alteration of obsidian and subsequent hydration rind damage is likely to occur where obsidian artifacts are directly exposed to prescribed and wildland fire conditions.


THE DOME FIRE OBSIDIAN STUDY: INVESTIGATING THE INTERACTION OF HEAT, HYDRATION, AND GLASS GEOCHEMISTRY By Anastasia Steffen, asteffen@vallescaldera.gov, DISSERTATION Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Anthropology, The University of New Mexico Albuquerque, New Mexico, July, 2005

ABSTRACT: This research integrates the analysis of obsidian geochemistry with investigation of the effects of forest fires on obsidian artifacts in surface assemblages. The first component of this project investigated the nature of heat altered obsidian at a prehistoric quarry site following the 1996 Dome Fire in the Jemez Mountains of northern New Mexico. Burned artifacts were examined to discern indicators of heat alteration in obsidian and to measure the impact of the fire on obsidian hydration (OH) bands. Descriptive categories developed to encompass a range of fire effects are provided here as a tool for identifying heat-altered obsidian in archaeological contexts. Measurement of obsidian hydration in artifacts collected from across the site demonstrate substantial loss and alteration of OH information, as well as positive correlation of OH loss/alteration with degree of burn severity.

The second component of the project investigated the role of obsidian geochemistry in fire effects, especially obsidian vesiculation. Intrasource and intersource geochemical analyses of obsidian trace element composition were integrated with analysis of major/minor elements, and with analysis of the water content as a volatile constituent. Results show elemental homogeneity among the Dome area Obsidian Ridge/Rabbit Mountain obsidians of the Cerro Toledo Rhyolite (CTR), demonstrate a cogenic relationship among geographically separate CTR deposits, and confirm that these obsidians are chemical distinct from Valles Rhyolite (VR) glasses at Cerro del Medio. Analyses of obsidian water content using loss-on-ignition (LOI) and infrared spectroscopy (FTIR) demonstrate the efficacy of both techniques for archaeological applications. Water contents were found to be low in VR samples, but high and variable in CTR samples. These results accord with the expectation of higher and more variable water contents in glasses from pyroclastic deposits, as compared with lower water contents in obsidians from extrusive volcanic contexts. This study provides a new example in which obsidian water content is high and variable within a single chemical type. This example provides support for the inclusion of water content as a compositional variable in the OH dating model and demonstrates the utility of integrating analysis of both elemental and volatile composition into archaeological practices of obsidian geochemical analyses.

Fire Effects to Obsidian - Loyd, J. M., Origer, T. M., and Fredrickson, D. A., (Eds.), The Effects of Fire and Heat on Obsidian. Papers presented in Symposium 2 The Effects of Fire/Heat on Obsidian at the 33rd Annual Meeting of the Society for California Archaeology April 23-25, 1999 Sacramento, California. Bureau of Land Management.  To download a short (260K) additional erratum sheet, click HERE

    Benson, A., 2002. Meadow Canyon Prescribed Burn: Effects of Fire on Obsidian Hydration Bands

    Deal, K., and McLemore, D., 2002. Effects of Prescribed Fire on Obsidian and Implications for Reconstructing Past Landscape Conditions.

    Halford, F. K., and Halford, A. S., 2002. The Trench Canyon Prescribed Burn: An Analysis of Fire Effects on Archaeological Resources within the Sagebrush Steppe Community.

    Jones, T., 2002. The Effect of Heat on Obsidian Density.

    Kelly, R. E., 2002. An Overview of Obsidian Studies within Western U.S. Parks.

    Loyd, J. M., 2002. Rehydration of burned obsidian.

    Nakazawa, Y., 2002. An Experimental Examination for Detecting Rhermal Traits on Obsidian Artifacts.

    Origer, T. M., 2002. Introduction.

    Schroder, S.-A., 2002. A synthesis of previous studies that explored the effects of fire on obsidian: where we've been and where we're going.

    Shackley, M.S., and C. Dillian. 2002. Thermal and environmental effects on obsidian geochemistry: experimental and archaeological evidence

    Siefkin, N., 2002. Manual fuel load reduction as a means of reducing the effects of fire on obsidian hydration: An example from Lassen Volcanic National Park.

    Skinner, C. N., 2002. Fire Regimes and Fire History: Implications for Obsidian Hydration Dating

    Smith, J., 2002. Protecting archaeological sites with prescribed fire.

    Steffen, A., 2002. The Dome Fire Pilot Project: Extreme Obsidian Fire Effects in the Jemez Mountains.

International Association for Obsidian Studies Great information on Obsidian

Specific issues with fire articles:

No. 12 (Summer 1994)

Inyo National Forest Plan to Test the Effects of Fire on Obsidian

Origer, T. M., and Anderson, J., 1994. Preliminary results on an assessment of the effects of fire on obsidian specimens from CA-SON-48, Salt Point State Park, Sonoma County, California. p 3-4.

No. 19 (Summer 1997) - Anderson, J., and Origer, T. M., 1997. Abstracts and Annotations of Reports and Publications Technotes: Adding a Little Fuel to the Fire: Some Thoughts on Fire and Obsidian Hydration.

No. 20 (Summer 1998) Origer, T. M., Loyd, J., and Schroder, S., 1998. Cooked Obsidian. International Association For Obsidian Studies Bulletin 20, p 10.

No. 35 (Summer 2006) - Fire Effects during the Valle Toledo Prescribed Burn

Publications involving obsidian and fire from Northwest Research Obsidian Studies Laboratory, Corvallis, Oregon

Skinner, Craig E., M. Kathleen Davis, and Thomas M. Origer. 1995. X-Ray Fluorescence Analysis and Obsidian Hydration Rim Measurements of Artifact Obsidian and Basalt from the Cottonwood Fire Mitigation Project, Tahoe National Forest, California. Report 1995-58 prepared by Northwest Research Obsidian Studies Laboratory, Corvallis, Oregon.

Skinner, C.E., J.J. Thatcher, and M.K. Davis. 1996. X-Ray Fluorescence Analysis and Obsidian Hydration Rim Measurement of Artifact Obsidian from 35-Ds-193 and 35-Ds-201 Surveyor Fire Rehabilitation Project, Deschutes National Forest, Oregon,. Northwest Research Obsidian Studies Laboratory Report 98-96, Corvallis, OR. Prepared for the Deschutes National Forest, Bend, Oregon, by Northwest Research Obsidian Studies Laboratory, Corvallis, Oregon.

Skinner, Craig E. and Jennifer J. Thatcher. 2003. X-Ray Fluorescence Analysis and Obsidian Hydration Measurement of Artifact Obsidian from Two Isolate Artifacts Associated With the Murray Fire, Ochoco National Forest, Grant County, Oregon. Report 2003-68 prepared for Archaeological Investigations Northwest, Inc., Portland, Oregon, by Northwest Research Obsidian Studies Laboratory, Corvallis, Oregon.

Additional Obsidian References

Benson, A., Effects of Fire on Obsidian Hydration Rind Thickness. Annual Meeting of the Society for California Archaeology, 1999. 

Benson, A., Effects of Low, Moderate, and Heavy Fuel Loads on Obsidian Hydration Rinds During a Prescribed Burn on the Tonopah Ranger District, Humbolt-Toiyabe National Forest. Annual Meeting of the Society for California Archaeology, Sacramento, 1999. 

Burton, J. F., 1996. An Archeological Survey of a Navy F-18 Crash Site: Hunter Mountain, Death Valley National Park, California. National Park Service, Western Archeological & Conservation Center, Tucson. 

Davis, L., Aaberg, S., and Johnson, A., 1992. Archeological Fieldwork at Yellowstone's Obsidian Cliff. Park Science Spring 1992, 26-27.

Davis, L. B., Aaberg, S. A., Schmitt, J. G., and Johnson, A. M., 1995. The Obsidian Cliff Plateau Prehistoric Lithic Source, Yellowstone National Park, Wyoming. National Park Service, Denver. 

Deal, K., Fire Histories, Fuel Loads and Obsidian: Preliminary Results of a Prescribed Burn Experiment on the Eldorado National Forest. California Fuels Committee Meeting, Placerville, California, 1997. 

Deal, K., 2001. Archaeological Investigations at Thirteen Sites within the Cleveland Fire. USDA Forest Service, Pacific Southwest Region, Eldorado National Forest, Pacific Ranger District, Placerville, California.  CD

Deal, K., 2001. Field Guide for Recording Fire Intensity, Fire Severity, and Fire Effects on Prehistoric Sites in the North-Central Sierras (Appendix D). In: Deal, K., (Ed., Archaeological Investigations at Thirteen Sites within the Cleveland Fire, Pacific Ranger District, Eldorado National Forest. Pacific Ranger District and Western Archeological & Conservation Center, Tucson, Placerville, California. CD

Deal, K. 2001. Fire Effects to Lithic Artifacts. in Cultural Resources Protection and Fire Planning, Tucson, Arizona.

Findlow, F. J., Martin, P. M., and Ericson, J. E., 1982. An Examination of the Effects of Temperature Variation on the Hydration Characteristics of Two California Obsidians. North American Archaeologist 3, 37-49.

Green, D. F., Re-hydrated Obsidian Projectile Points on the Warner Mountains, California. Annual Meeting of the Society for California Archaeology, 1999. 

Green, D. F., Bordwell, K., Hall, R., and Goheen, A., 1997. Effects of Prescribed fire on obsidian hydration rates. USDA Forest Service, Warner Mountain Ranger District, Modoc National Forest. 

Jackson, R. J., 1984. Current Problems in Obsidian Hydration Analysis. In: Hughes, R. E., (Ed.), Obsidian Studies in the Great Basin. Department of Anthropology, University of California, Berkeley, pp. 103-115.

Jones, A. T., and Ryan, K. C., ca. 2001. Wildland Fire in Ecosystems: Effects of Fire on Cultural Resources and Archeology. USDA Forest Service, Rocky Mountain Research Station, Fort Collins, Colorado. 

Linderman, C. A., 1992. The effects of fire on obsidian artifacts: A problem in hydration dating in a woodland environment, University of Oregon, Department of Anthropology, Eugene. 

Linderman, C. A., and Bergland, E. O., 1991. The effects of fire on obsidian artifacts: 1989 regional forester's challenge grant study. USDA Forest Service, Pacific Northwest Region, Willamette National Forest, McKenzie Ranger District, McKenzie Bridge, Oregon. 

Lissoway, J., and Propper, J., 1990. Effects of fire on cultural resources. In: Krammes, J. S., (Ed.), Effects of Fire Management of Southwestern Natural Resources: Proceedings of the Symposium, November 15-17, 1988, Tucson, AZ. USDA Rocky Mountain Forest and Range Experiment Station, Fort Collins, Colorado, pp. 1-10.

Mazer, J. J., Stevenson, C. M., Ebert, W. L., and Bates, J. K., 1991. The experimental hydration of obsidian as function of relative humidity and temperature. American Antiquity 56, 504-513.

Nakazawa, Y., Thermal alteration of obsidian: experiments, classification and method for detection. Annual Meeting of the Society for California Archaeology, 1999. 

Origer, T. M., and Fredrickson, D. A., ca. 2000. The Effects of Burning on Obsidian. Bureau of Land Management. 

Rowney, M., and J.P. White. 1997. Detecting Heat Treatment of Silcrete: Experiments with Methods. Journal of Archaeological Science 24:649-657.

Ruscavage-Barz, S. M., 1999. Fire in the Hole: The Effects of Fire on Subsurface Archaeological Materials (Draft). National Park Service, Bandelier National Monument, New Mexico. 

Shackley, M. Steven and Dillian, Carolyn, Thermal and Environmental Effects on Obsidian Geochemistry: Experimental and Archaeological Evidence

Siefkin, N., and Brunmeier, P., Coping with Conflagrations: The 1999 Archeological Prescribed Fire Survey at Lava Beds National Monument. The 1999 Northern Data Sharing Meeting of the Society for California Archaeology, 1999.

Solomon, M., Fire and glass: the effects of prescribed burning on obsidian hydration bands. Annual Meeting of the Society for California Archaeology, 1999. 

Solomon, M., 2000. An Assessment of the Potential Effects to Obsidian Hydration Bands Caused by Prescribed Fires. Prepared for: California Department of Forestry and Fire Protection, Archaeology Program, PO Box 944246, Sacramento, California 94244-2460 contract number 8CA97015. 

Steffen, A., When obsidian goes bad...: forest fire effects on Jemez Obsidian. Annual Meeting of the Society for American Archaeology, 1999. 

Steffen, A., 2005. The Dome Fire Obsidian Study: Investigating the Interaction of Heat, Hydration, and Glass Geochemistry, The University of New Mexico, Albuquerque, New Mexico. 

Stevenson, C. M., Carpenter, J., and Scheetzs, B. E., 1989. Obsidian dating: recent advances in the experimental determination and application of hydration rates. Archaeometry 31, 193 - 206.

Stevenson, M. C., Bates, J. K., Abrajano, T. A., and Scheetz, B. E., 1989. Obsidian and basaltic glass dating require significant revision of high temperature rate development methods. Society for Archaeological Sciences Bulletin 12, 3-5.

Timmons, R. S., 1999. Fire effects on prehistoric artifacts: Northern Region/Intermountain Research Station experiments preliminary research design for assessing site impacts, pp. 8 pp. 

Trembour, F., and Friedman, I., 1984. Obsidian hydration dating and field site temperature. In: Hughes, R. E., (Ed.), Obsidian studies in the Great Basin, pp. 79-90.

Trembour, F. N., 1990. Appendix F. A hydration study of obsidian artifacts, burnt vs unburnt by the La Mesa Forest Fire. In: Traylor, D., Hubbel, L., Wood, N., and Fiedler, B., (Eds.), The 1977 La Mesa Fire Study: An investigation of fire and fire suppression impact on cultural resources in Bandelier National Monument. National Park Service, Division of Anthropology, Branch of Cultural Resources Management, Santa Fe, pp. 174-190.

Waechter, S. A.,  Big Fire Small Fire: the Effects of Burning on Flaked Stone Artifacts -CDF publication on fire's effects to obsidian

Welch, P., and Gonzales, T., 1982. Research design, prescribed burn impact, evaluation upon cultural resources, LMDA and Thing Mountain Chaparral Management Projects. USDA Forest Service, Cleveland National Forest, pp. 1-9. 

Wilbur, R., The burning question: report on the effect of burn management projects on obsidian hydration rims. the Society for California Archaeology Annual Meetings, 1988. 



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