Many visitors to the American South West come back with turquoise jewellery: the Native American people of Arizona and New Mexico exploited local sources, and modern craftsmen have developed a prosperous industry. Thirty years ago the archaeological scientists Garman Harbottle and Edward Sayre used neutron activation analysis to show that turquoise mosaics from Mexico, found as far away as the great Maya city of Chichén Itzá in Yucatan and dating back to around AD900, used raw material originating in the Cerrillos mines between Albuquerque and Santa Fe in New Mexico, an overland distance of some 3,200 km (2,000 miles). It was assumed that the Cerrillos mines had also supplied more local demand, for instance from the Chaco Canyon communities west of Santa Fe. A new technique of source characterisation, using hydrogen and copper isotope ratios established by secondary ion mass spectrometry (SIMS), shows that this picture was altogether too simple.
Sharon Hull and her colleagues report in the Journal of Archaeological Science this month that of eleven samples from Chaco Canyon sites, dating from AD550 to 1050, only two could be attributed to the Cerrillos source. Two others came from Orogrande in southern New Mexico, three from the No 8 Mine in northern Nevada, and one from the Montezuma source in southern Nevada.
Although none of the Mexican mosaics has yet been re-examined in detail, this looks like a good idea: not only the Chichén Itzá pieces, but Aztec turquoise mosaics, such as those in the British Museum’s Mexican Gallery, could well yield evidence that ancient trade networks in late pre-Columbian America were much more complex than we have assumed.
Journal of Archaeological Science 35; 1355-1369
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