https://www.nationalgeographic.com/magazine/2020/03/how-spains-pulpi-geode-formed-chess-grand-master-workout-and-viking-berserke

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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... Full story

14 February

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