You never know what you're going to get when you crack open a geode-like rock called an agate, but a new specimen is even more surprising than usual: It looks just like Cookie Monster. The agate, found in Soledade, a precious stone hotspot in southern Brazil, is a dead ringer for the blue, googly-eyed Sesame Street Muppet. After its owner, California mineral collector Mike Bowers, posted about the agate on Facebook, it went viral, with write-ups in newspapers from Australia to Israel to the United States. "I didn't realize that Cookie Monster was so well known and part of the...