Turritella agate is a fossiliferous agate that contains lots of snails who died, sank to the bottom of a lake, and became silicified. When it was first named, people thought the fossils were marine snails from the Turritella genus. The shells are actually from the freshwater snail Elimia tenera, but the Turritella name was too popular already and it stuck. They are found in the Green River Formation in southwestern Wyoming, northeastern Utah, and northwestern Colorado, because that’s where the snails used to live (they are extinct). This specimen is from the personal collection of Show-Me Rockhounds member David Reed. Fun fact: Elimia tenera snails became fossilized in materials other than agate, such as limestone, so there is also turritella limestone. It’s not quite as pretty in my opinion because the light background doesn’t contrast with the shells like agate does.