Beginning in the late 19th century, around a dozen carved skulls made of clear or milky white quartz—also known as rock crystal—made their way into private and public collections around the globe. Since then, the origins of these “crystal skulls” have been the subject of ongoing mystery and controversy.

According to the people who claimed to have discovered the skulls, they date back thousands or even tens of thousands of years, to ancient Mesoamerican civilizations such as the Aztec, Toltec, Mixtec or Maya. Many of those who believe in the crystal skulls’ ancient provenance attribute supernatural powers to the objects, including healing properties and the power to expand a person’s psychic abilities in their presence.

Some have linked the skulls to the lost city of Atlantis, or claimed them as proof that extraterrestrials visited pre-Columbian civilizations such as the Aztecs. The 2008 movie “Indiana Jones and the Kingdom of the Crystal Skull” capitalized on the ongoing mystery, as well as the passion the skulls’ believers bring to their side of the argument.

Scientists and archaeologists, on the other hand, are skeptical. For one thing, not one of the skulls was recovered on a documented excavation. And while skulls were a common motif in ancient Mesoamerica, and particularly Aztec, artwork (several Aztec gods are represented by skulls), the style and technique of the crystal skulls do not resemble genuine pre-Columbian representations of skulls.

Recently, scientists from the British Museum in London and the Smithsonian Museum of Natural History in Washington, D.C. conducted analyses of crystal skulls using electron microscopes. After finding markings that could only have been made by modern-day carving implements—rather than the stone, bone and wooden tools that would have been used in pre-Colombian times—they concluded that the skulls were likely fakes. The scientists believe they were probably manufactured in the late 1800s, in response to a surge of interest in the ancient world and its artifacts.