Scott Michlin welcomed me back to his radio show last month, and I came bearing tales of turquoise (click here to listen to our discussion). Sharon Hull (University of Manitoba, Department of Geological Sciences) and her colleagues recently finished a study of turquoise using a new sourcing method. Turquoise has been notoriously difficult to source, for a number of reasons, but I think it is fair to say that these researchers have cracked the turquoise code. Here’s Sharon:
North Americans have mined turquoise for more than 1,000 years! The procurement and trade of turquoise was as important to the inhabitants of ancient societies in the Greater Southwest and Mexico as gold is today. Archaeologists have recovered one million pieces of turquoise from archaeological sites throughout the Greater Southwest and Mesoamerica, but researchers have had difficulty reconstructing the spatial and temporal patterns of turquoise trade and procurement strategies.
For decades, archaeologists have sought to develop a technique that could identify the origins of turquoise artifacts using trace and rare earth element concentration patterns. These studies have met with limited success, however, due to the intrinsic limitations of these types of analyses for minerals such as turquoise, which varies in color and is chemically variable within a single sample or mine.
I am happy to report that my colleagues—Mostafa Fayek, Joan Mathien, and Heidi Roberts—and I have found a way to address this problem. To link turquoise artifacts to their geological source, we developed a technique using the isotope ratios of hydrogen and copper and the microanalytical abilities of a secondary ion mass spectrometer (SIMS). We then developed a comparative database consisting of more than 800 analyses from 22 turquoise resource areas in the western United States and northern Mexico. We also maintain a digital archive that contains the isotopic fingerprint of each turquoise artifact we analyzed, allowing us to examine turquoise procurement strategies from multiple perspectives and research focuses. For example, we can focus on particular sites (e.g., Chaco Canyon) or on a particular deposit (e.g., Halloran Springs), or we can compare the procurement patterns of contemporaneous sites or changes in these patterns through time.
This breakthrough technique is successful for several reasons. First, the hydrogen and copper isotopic signatures of turquoise are dictated by the geography and the geology of the turquoise deposits. Secondly, we use the in situ microanalytical capabilities of the secondary ion mass spectrometer (SIMS) to measure the isotopic ratios of the hydrogen and copper in turquoise. SIMS is capable of performing accurate isotopic measurements on very small samples. The small sample size required for analysis is particularly advantageous for analyzing precious archaeological artifacts. Thus, the technique is relatively nondestructive, and we can return turquoise artifacts to their original collections without apparent damage to their physical appearance.
In our most recent publication, we identified the geological source of turquoise artifacts from sites in Chaco Canyon, the northern San Juan basin, and Virgin Puebloan sites in Utah and Nevada. By comparing the procurement and exchange patterns of these sites, we were successful in identifying:
- Multiple trade networks in Chaco Canyon
- Different turquoise procurement strategies between Pueblo Bonito and the small sites at Marcia’s Rincon (on the south side of Chaco Canyon, opposite the visitors’ center)
- Similar procurement patterns for Pueblo Bonito and Aztec Ruins, and for the sites in Marcia’s Rincon and Salmon Ruin
- Links between turquoise found in the San Juan Basin and western turquoise deposits
- A possible link between the inhabitants of Marcia’s Rincon and the Virgin Pueblo region
- Virgin Pueblo sites that may be linked to the San Juan Basin via long-distance trade routes
Now we’re examining data from Mogollon sites located in the Hueco-Tularosa Basin, Cañada Alamosa, and the Villa Ahumada site in northern Mexico, where we have identified two possible turquoise trade routes—one from the west, and one that appears to follow along or near the Rio Grande Rift. We also plan to do additional work on samples from Mexico and southwestern New Mexico, and we will ultimately expand our research further south into Mexico, and possibly Chile.
For further reading:
Hull, S., M. Fayek, F. J. Mathien, and H. Roberts
2014 Turquoise Trade of the Ancestral Puebloan: Chaco and Beyond. Journal of Archaeological Science 45:187–195.
9 thoughts on “Turquoise Trade among Ancestral Pueblo Groups”
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Fascinating article. Be sure and look also at the Globe-Miami, Arizona area. We had a prehistoric turquoise mine in Pinto Valley.
How many (and which) pre-contact turquoise locations have you tested and recorded?
I haven’t been involved with turquoise for many years. My brother and I got into the jewelry “trade” some 40 years ago cutting turquoise. Having the technology to determine the origin of artifacts scientifically is an important breakthrough. I do believe however, that much of the materiel can be identified fairly accurately by persons that work with and are exposed to materiel from many sources. It does get difficult with pieces such as your example, without much matrix showing, the color is more difficult to identify as coming from a specific mine or area.
@Marc Severson: Thanks for the information on the Pinto Valley.
@Mark Bahti: Your question requires an in-depth response. Contact me at preed@archaeologysouthwest.org and I will put you in touch with Sharon Hull directly.
@Philip: Certainly, years of experience is a great asset for visually identifying-discriminating different sources of turquoise. This breakthrough, however, will remove much of the uncertainty and finally put turquoise sourcing on equal scientific ground with obsidian sourcing, among others.
@Marc Severson: We are actually using turquoise from the Sleeping Beauty mine for one of our standards. It is one of the most homogenous low-iron samples!
@ Mark Bahti: We have 22 turquoise deposits in our comparative database. I just received some good samples from Mexico and from southwestern New Mexico. I hope to analyze them this summer and add them to the database. You can e-mail me directly (hull.sharon.2012@gmail.com) and I can send you the information on the deposits that are currently in our database.
@Philip F. Taccetta: The ability to identify the geological source of turquoise is pretty controversial. Although some turquoise (e.g., Bisbee) is more distinguishable than others, we found turquoise from light to dark green, light to dark blue, and all shades in-between at many of the mines including Cerrillos Hills (New Mexico), Royston Hills (Nevada), and the King Manassa (Colorado). We also found that many of the samples in museum collections that are “labeled” turquoise are not chemical or mineralogical turquoise. After so many years looking at turquoise, I still can’t always confirm that a blue-green sample is turquoise just by visual inspection! I think the long-time turquoise jewelers are much better at it than I am!
Have you or has anybody ever considered the
Zuni Turquoise mine(s)in the Zuni Mountains? Frank Cushing visited these in the winter of 1879; not the best time of the year, and apparently the mine was no longer being utilized. See Jesse Green’s book Cushing at Zuni (1990) pp. 66+
@John P Wilson: I have heard of the Zuni mines, but was not able to find any information on them or their location in the literature. I would be very happy to receive any information on the mine Especially, location!
Just a quick note: The image of the turquoise artifact was not from Pueblo Bonito. When we visited AMNH to collect turquoise artifacts for analyses, someone else was photographing artifacts. I just assumed that they were all from Pueblo Bonito. Please forgive my assumption and error! The piece that was posted was actually from Canyon del Muerto and was collected by Earl Morris.
I am very familiar with Cushing’s chalchihuitl mines in the Zuni Mountains as I once helped establish a mining claim there for Zuni friends. The material from this location is actually malachite and azurite which my Zuni friends use for religious paint rock and fetish carving material. Of course it is important to remember that “chalchiuitl” actually translates out as “precious green stone” and not necessarily turquoise.