Surprise over Aztec turquoise

Valuable mineral was not imported

Blue-green patterns: Turquoise was very popular with Aztecs, Maya and others. © Frances F. Berdan
Read out

Blue-green treasure: Early American advanced civilizations such as the Aztecs considered turquoise to be a valuable gem - but they do not seem to have imported this mineral from today's southwestern US, researchers have long thought. Instead, isotopic analyzes of archaeological finds suggest that the mineral could come from the home region of the Aztecs themselves. This not only sheds new light on the then availability of turquoise, but also on the long-distance trade relations of the Mesoamerican peoples.

Turquoise was considered extremely valuable in many Mesoamerican civilizations. Peoples such as the Aztecs and the Mayans used the blue-green mineral for ritual purposes, works of art and wall decorations - as evidenced by numerous archaeological artifacts. But where did the turquoise come from, which the early societies of Central America wanted as gems?

Many researchers believe that the mineral was an imported product from prehistoric mines in the southwest of today's US and adjacent areas of northern Mexico. For one thing, no turquoise deposits are known from the homeland of Aztecs and Co. On the other hand, these peoples demonstrably drove lively trade with cultures from the southwest - for example with the Hohokam and the Mogollon Indians.

Mosaic from the Templo Mayor © Oliver Santana

Telltale isotope ratio

But is this theory correct? The clear evidence that Mesoamerican civilizations actually imported their turquoise was still pending. To change this, Alyson Thibodeau from Dickinson College, Carlisle, and colleagues have taken a closer look at some of the artifacts of these cultures: they examined turquoise tesserae of shields, masks, and other objects.

Of the analyzed platelets, 43 were from Templo Mayor, the sacred center of the Aztec capital, Tenochtitlan, and five were relics of the Mixtec culture. For all these stones, the researchers were particularly interested in the isotopic composition. For the ratio of isotopes such as lead and strontium can provide clues to the surrounding rock, in which the turquoise mineral was once included. display

Ornate Mixtec mask Alyson M. Thibodeau

Unexpected origin

Overall, the team of scientists managed to obtain meaningful data on the ratio of lead and strontium isotopes for 31 samples. The surprise: in 29 cases, this was not consistent with the pattern typical of the US southwestern turquoise. Instead, the data pointed to a very different geological origin.

As Thibodeau and her colleagues report, the isotope ratio is closer to those of copper deposits and crustal rocks from the home of the Aztecs and Mixtecs themselves. Although the researchers can not determine the exact source of turquoise mineral. But it is clear that the peoples obviously did not import their turquoise from far away. "The results thus revise our earlier concept and provide new insights into the mineral's availability at that time, " notes Thibodeau.

At the same time, the findings shed new light on the trade relations of the Mesoamerican cultures: "Perhaps T rkis was not such an important part of the long-distance trade between the southwest and Mesoamerica, " concludes the research team. (Science Advances, 2018; doi: 10.1126 / sciadv.aas9370)

(AAAS / Dickinson College, 14.06.2018 - DAL)