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Every beach’s sand has its own unique sound ‘signature’

Sand from different beaches has its own unique sound—and researchers have figured out how to listen in, The Economist reports. Sand, which is a valuable commodity, is often taken illegally for construction projects and artificial beaches. (India even has its own “sand mafia.”) To find out where a sample of sand comes from, scientists drop it in acid, which breaks down the sand’s carbonate chemicals (made from the shells of long-dead sea creatures) into carbon dioxide bubbles. Using sensitive listening devices, the researchers measure how the bubbles change the way sound travels through the mixture—yielding a unique frequency. When scientists listened to sand samples from several different beaches in the Netherlands, they found that each had a unique signature, they report in Applied Acoustics. Future research might address a more pressing philosophical question: If sand falls in acid with no one there to hear it, does it still make a sound?

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