アメリカ自然史博物館さんのインスタグラム写真 - (アメリカ自然史博物館Instagram)「Today’s Exhibit of the Day? The Museum’s giant amethyst geode. Standing 9 ft (2.7 m) tall and weighing around 11,000 lbs (5,000 kg), it’s one of the largest specimens in our halls. How did this dazzling geode come to be? About 135 million years ago, the continental plates carrying South America and Africa began to separate. Magma poured out from fractures in Earth’s crust and large gas bubbles escaped from within the magma—becoming 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. Spot this and other amazing specimens in the Museum’s Mignone Halls of Gems and Minerals! Photo: D. Finnin/ © AMNH #museum #nyc #geology #geode #science #stem #didyouknow」10月14日 22時01分