amnhnyc: If you visited the Museum in 2018, you may remember a 12-foot-tall glittering amethyst geod

amnhnyc:

If you visited the Museum in 2018, you may remember a 12-foot-tall glittering amethyst geode, standing in the Grand Gallery. But did you know the new Mignone Halls of Gems and Minerals, which opens on June 12, will feature another giant geode, too? The second, which stands 9 feet tall, will be on view at the entrance to the new galleries. It weighs around 12,000 pounds (5,440 kg), or about as much as four black rhinos!

How did dazzling geodes such as this one come to be? About 135 million years ago, a geological drama set the stage for them to form. As the continental plates carrying South America and Africa began to separate, magma poured out from fractures in Earth’s crust. Large gas bubbles escaping from within the magma were trapped in the rock as it solidified, forming cavities. Groundwater flowing into these spaces brought dissolved silica, which crystallized into quartz. Over millennia, most of these quartz crystals turned into rich purple amethyst.
Photo: D. Finnin/© AMNH (at American Museum of Natural History)
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