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Geologist Milagros Carretero sits inside the Pulpí Geode, one of the world’s largest geodes.

How to cook a violent Viking stew—and a giant geode

Scientists discover recipes for some of the world’s toughest concoctions—and a way to burn off 6,000 calories without strenuous activity.

These stories appear in the March 2020 issue of National Geographic magazine.

A giant among geodes

Any geode might make us wonder: What geologic forces form these hollows lined with crystals? But the Pulpí Geode, discovered in an abandoned Spanish mine, takes wonder to a different scale. One of the world’s largest geodes, it’s an approximately 390-cubic-foot cavity whose walls bristle with imposing gypsum crystals, some nearly seven feet long. Now scientists are hoping to uncover how these colossal crystals developed.

They seem to have been made by a very specific recipe: a 250-million-year-old supply of the mineral anhydrite, a climate hospitable to crystal formation, and lots of water and time. In the resulting chemical soup, larger crystals may have cannibalized smaller ones to boost their own size, while swings in the local temperature could have accelerated the crystal growth even further.

Though key chapters remain incomplete, this otherworldly site now has a possible origin story. —Robin George Andrews

(For more on the giant crystals and their astrobiology implications, check out our podcast, Overheard at National Geographic.)

The grand master workout

Though chess is hardly a strenuous sport, its grand masters experience physical costs on a par with those faced by more active athletes. Because of the human body’s response to the stress of elite play, chess professionals can burn up to 6,000 calories a day in tournaments, a Stanford University researcher says.—Annie Roth

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Did this plant help Vikings lose control?

The English word “berserk” is derived from berserkers, violent Vikings said to consume something that induced rage before battle. Historians have long assumed that fly agaric, a hallucinogenic mushroom, was the berserkers’ drug of choice. But now ethnobotanist Karsten Fatur says Vikings likely took henbane (below). The plant is more common in Scandinavia than fly agaric, he says, and has compounds with greater links to aggression. —A.R.

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