Huge, milky-white beams of gypsum (CaSO4·2H2O) fill the Cave of Crystals near Naica, Mexico. For nearly a million years, conditions within the cave 290 m underground were perfect for the growth of the crystals, allowing them to reach massive sizes. Scientists are now studying how to protect and preserve the crystals for future generations.
Credit: Alexander Van Driessche/Wikimedia Commons
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