Aztec duck-head pendants recovered from Tenochtitlán were made using volcanic glass called obsidian. - Mirsa Islas/Courtesy Proyecto Templo Mayor, INAH ...

The Aztec Empire once hosted an expansive trade ... The 788 precious obsidian objects analyzed include weapons, urns, earrings, pendants, scepters, and decorated human skulls.

The discovery also sheds light on how the Aztec society evolved — introducing more standardized religion and control before the empire fell in 1521 — by showing how obsidian use changed over time.