"Turritella Agate" is the name given to a brownish gem material that contains spectacular fossil snail shells entombed in a semitransparent agate. It is possibly the best-known fossil from the Green River Formation. When the Green River was being deposited, the spiral-shaped shells accumulated in the sediments of the shallow inland sea. A few lenses of this snail-bearing sediment were then agatized by the deposition of fine-grained silica (chalcedony - also known as agate) into the cavities of the shells and the voids between them. If the sediment was completely agatized, it has potential lapidary (gem cutting) potential.
Although millions of people have called this material "Turritella" for several decades, the name is actually incorrect. Somehow it acquired the Turritella name after a genus of fossil snails that are very similar to the shells in the agate. The proper name of the snails is "Elimia tenera," a member of the Pleuroceridae family. Perhaps a better name would be "Elimia Agate" which is not quite as elegant.
To learn more about the Turritella - Elimia naming error, visit the Museum of the Earth website, which is authored by the Paleontological Research Institution - people who know what they are talking about when it comes to fossils.
More Fossils! Plants, Insects, Fish
Green River fossil turtle: This ten-inch-long turtle belongs to the Baenidae family, an extinct North American group. Shell characteristics, a very long tail and recurved claws suggest they were strong bottom-walking turtles. National Park Service photo. Enlarge image.