According to Discover Magazine, there were carved crystal skulls in the inventory of major museums and institutions all over the world. As recently as the 1990s, they were believed to be genuine ancient artifacts from the Aztec Empire. Skulls figured prominently in Aztec culture, as did works of art reflecting high levels of artisanship. For these reasons, skulls carved from crystal dating from the Aztec Empire seemed plausible to both researchers and academics.
In the ’90s, however, anthropologist Jane Walsh of the Smithsonian’s National Museum of Natural History grew suspicious about the authenticity of the objects. Confirming her concerns, among other evidence: the proportions were off; the carving was done with tools contemporary to the mid-to-late 19th century, rather than the 14th through 15th century, when the Aztecs ruled much of what is now Mexico (according to World History). Further investigation led Walsh to the name Eugène Boban, a 19th-century fan of Mexican history and self-taught archaeologist.
Turns out that after establishing himself as an “expert” in the field, Boban was able to “authenticate” fake skulls, selling forgeries to museums all over the world. While it’s now agreed the crystal skulls aren’t real — put it another way, they’re real fakes — no one knows for sure how the skulls were carved, or by whom. That part of the mystery, at least, remains to be solved in an Indiana Jones movie of the future.