Obsidian - Volcanic Glass Prized for Stone Tool Making

What Makes Obsidian Such a Prize?

Obsidian Outcrop, Obsidian Trail in Newberry Volcanic Monument, Oregon
Obsidian Outcrop, Obsidian Trail in Newberry Volcanic Monument, Oregon. B.D.'s World

The volcanic glass called obsidian was highly prized in prehistory where ever it was found. The glassy material comes in a range of colors from black to green to bright orange, and it is found everywhere rhyolite-rich volcanic deposits are found. Most obsidian is a deep rich black, but, for example, pachuca obsidian, from a source in Hidalgo and distributed throughout Mesoamerica during the Aztec period, is a translucent green color with a golden yellow sheen to it. Pico de Orizaba, from a source in southeastern Puebla is almost completely colorless.

Obsidian Qualities

The qualities that made obsidian a favorite trade item are its shiny beauty, its easily worked fine texture, and the sharpness of its flaked edges. Archaeologists are fond of it because of obsidian hydration---a relatively secure (and relatively low cost) way to date the period an obsidian tool was last flaked.

Sourcing obsidian--that is to say, discovering where the raw stone from a particular obsidian artifact came from--is typically conducted through trace element analysis. Although obsidian is always made up of volcanic rhyolite, each deposit has slightly different amounts of trace elements in it. Scholars identify the chemical fingerprint of each deposit through such methods as X-ray fluorescence or neutron activation analysis and then compare that to what is found in an obsidian artifact.

Alca Obsidian

Alca is a type of obsidian that is solid and banded black, gray, maroon brown and bottled black maroon brown, that is found in volcanic deposits in the Andes mountains between 3700-5165 meters (12,140-16,945 feet) above sea level. The largest known concentrations of Alca are at the east rim of the Cotahuasi Canyon and in the Pucuncho basin. The Alca sources are among the most extensive sources of obsidian in South America; only the Laguna de Maule source in Chile and Argentina has comparable exposure. 

Three types of Alca, Alca-1, Alca-5 and Alca-7, outcrop on the alluvial fans of the Pucuncho basin. These cannot be discerned with the naked eye, but they can be identified on the basis of geochemical characteristics, identified through ED-XRF and NAA (Rademaker et al. 2013). Stone tool workshops at the sources in the Pucuncho basin have been dated to the Terminal Pleistoceneand stone tools dated to the same 10,000-13,000 year range have been discovered at Quebrada Jaguay on the coast of Peru.


For information on dating obsidian , see the article on obsidian hydration. See the History of Glass Making, if that's what interests you. For more rock science on the substance, see the geology entry for obsidian.

For the heck of it, try the Obsidian Trivia Quiz.

Freter A. 1993. Obsidian-hydration dating: Its past, present, and future application in Mesoamerica. Ancient Mesoamerica 4:285-303.

Graves MW, and Ladefoged TN. 1991. The disparity between radiocarbon and volcanic glass dates: New evidence from the island of Lanai, Hawaii. Archaeology in Oceania 26:70-77.

Hatch JW, Michels JW, Stevenson CM, Scheetz BE, and Geidel RA. 1990. Hopewell obsidian studies: Behavioral implications of recent sourcing and dating research. American Antiquity 55(3):461-479.

Hughes RE, Kay M, and Green TJ. 2002. Geochemical and Microwear Analysis of an Obsidian Artifact from the Brown Bluff Site (3WA10), Arkansas. Plains Anthropologist 46(179).

Khalidi L, Oppenheimer C, Gratuze B, Boucetta S, Sanabani A, and al-Mosabi A. 2010. Obsidian sources in highland Yemen and their relevance to archaeological research in the Red Sea region. Journal of Archaeological Science 37(9):2332-2345.

Kuzmin YV, Speakman RJ, Glascock MD, Popov VK, Grebennikov AV, Dikova MA, and Ptashinsky AV. 2008. Obsidian use at the Ushki Lake complex, Kamchatka Peninsula (Northeastern Siberia): implications for terminal Pleistocene and early Holocene human migrations in Beringia. Journal of Archaeological Science 35(8):2179-2187.

Liritzis I, Diakostamatiou M, Stevenson C, Novak S, and Abdelrehim I. 2004. Dating of hydrated obsidian surfaces by SIMS-SS. Journal of Radioanalytical and Nuclear Chemistry 261(1):51–60.

Luglie C, Le Bourdonnec F-X, Poupeau G, Atzeni E, Dubernet S, Moretto P, and Serani L. 2006. Early Neolithic obsidians in Sardinia (Western Mediterranean): the Su Carroppu case. Journal of Archaeological Science 34(3):428-439.

Millhauser JK, Rodríguez-Alegría E, and Glascock MD. 2011. Testing the accuracy of portable X-ray fluorescence to study Aztec and Colonial obsidian supply at Xaltocan, Mexico. Journal of Archaeological Science 38(11):3141-3152.

Moholy-Nagy H, and Nelson FW. 1990. New data on sources of obsidian artifacts from Tikal, Guatemala. Ancient Mesoamerica 1:71-80.

Negash A, Shackley MS, and Alene M. 2006. Source provenance of obsidian artifacts from the Early Stone Age (ESA) site of Melka Konture, Ethiopia. Journal of Archaeological Science 33:1647-1650.

Peterson J, Mitchell DR, and Shackley MS. 1997. The social and economic contexts of lithic procureent: obsidian from classic-period Hohokam sites. American Antiquity 62(2):213-259.

Rademaker K, Glascock MD, Kaiser B, Gibson D, Lux DR, and Yates MG. 2013. Multi-technique geochemical characterization of the Alca obsidian source, Peruvian Andes. Geology 41(7):779-782.

Shackley MS. 1995. Sources of archaeological obsidian in the Greater American southwest: An update and quantitative analysis. American Antiquity 60(3):531-551.

Spence MW. 1996. Commodity or gift: Teotihuacan obsidian in the Maya region. Latin American Antiquity 7(1):21-39.

Stoltman JB, and Hughes RE. 2004. Obsidian in Early Woodland Contexts in the Upper Mississippi Valley. American Antiquity 69(4):751-760.

Summerhayes GR. 2009. Obsidian network patterns in Melanesia: Sources, characterisation, and distribution. IPPA Bulletin 29:109-123.

Also Known As: Volcanic glass

Examples: Teotihuacan and Catal Hoyuk are just two of the sites where obsidian was clearly considered an important stone resource.