In November 1986, Australian miners climbed Lunatic Hill and bored 20 meters into the Earth. They were rewarded with a fist-sized, record breaking gemstone, which they named the Hailey’s Comet opal. Thanks to a characteristic called “play of color,” no two opals look the same. So what causes these vibrant displays? Jeff Dekofsky digs into the rock’s shimmering, dancing displays of light.