WASHINGTON — Grab the whip and put on that hat. Right in step with the newest Indiana Jones movie, the National Museum of Natural History is unveiling its very own crystal skull Thursday, along with a documentary film on cable TV'S Smithsonian Channel.

The quartz skull — a milky white giant at 31 pounds and nearly 10 inches high — came to the Smithsonian Institution in 1992 with an anonymous note saying it was purchased in Mexico in 1960 and that it was Aztec in origin.

Rick McKay/Washington Bureau (ENLARGE)

Crystal skulls have been a mystery since they first started appearing in prestigious museums and auction houses. Above, the Smithsonian's version.

Rick McKay/Washington Bureau (ENLARGE)

Jane MacLaren Walsh said that despite the fact she did not find a real Mesoamerican artifact, she has enjoyed working with the skull.

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Crystal skulls have been a mystery since they first started appearing in prestigious museums and auction houses, including Tiffany and Co., in the early 20th century.

With no scientific evidence to prove otherwise, the skulls were widely accepted as artifacts from the era before Christopher Columbus arrived in the Americas, created by native cultures such as the Mayans and Aztecs who practiced human sacrifice.

But Smithsonian anthropologist Jane MacLaren Walsh, an expert in Mexican archaeology, didn't believe it. In 1996 she sent the skull for electron microscopy tests.

Even though the skull looks perfectly smooth, the high magnification clearly showed marks made by modern-day tools.

One after another, crystal skulls from other museums around the world were examined and proved to be recent creations. Since no authentic crystal Mesoamerican skull has ever been found, Walsh said at a news conference Wednesday, the skulls could be called inventions instead of fakes.

Walsh said that despite the fact she did not find a real Mesoamerican artifact, she has enjoyed working with the skull.

"I am still amazed after 16 years of looking at it," she said.

According to Walsh, the Smithsonian's skull was probably created shortly before it was purchased in 1960.

"This one is definitely a '60s skull — it is big and bold," she joked.