Turquoise is nearly synonymous with Arizona. It’s the state’s gemstone.

For more than a century, it was thought that turquoise used by ancient civilizations in Mesoamerica — the region ranging from central Mexico to Central America — originated from the American Southwest and was imported by the civilizations to the south.

But collaborative study and geochemical analysis by a team including UA geologists and anthropologists revealed that the geologic source of Aztec and Mixtec turquoise is actually within Mesoamerica.

How do they know?

UA College of Science Dean Joaquin Ruiz, UA anthropologist David Killick and UA geosciences doctoral studies graduate Alyson Thibodeau, now at Dickinson College in Pennsylvania, and other collaborators measured the isotopic signatures of the Meosamerican turquoise artifacts of the Aztecs and Mixtecs.

Those signatures function like fingerprints to determine the stones’ geologic origins.

Specifically, the researchers analyzed lead and strontium isotopes on fragments of turquoise-encrusted mosaics, one of the most iconic forms of ancient Mesoamerican art.

The samples were from dozens of tiles excavated from within the Temple Mayor, the ceremonial and ritual center of the Aztec empire in present-day Mexico City.

The analyses showed that the turquoise’s isotopic signatures were consistent with the geology of Mesoamerica and not the Southwestern U.S.