Turritella Agate or Turritella Fossil is what this stone is usually called in the “market” and by “market” that means the jewelry makers and gem and mineral wholesalers. This name is actually incorrect. When it was initially discovered this material was thought to be the spiral-shaped gastropod (snail), turritella. What it really is is a freshwater snail called, Elimia tenera, which belongs to the Pleuroceridae family. The photo below shows the actual turritella (fossil shells). Personally, I wouldn’t know the difference but, what makes it important is that elimia tenera is extinct. The turritella is still found along the coastline of beaches.
Photo credit: By Wilson44691 – Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=5526735
Photograph of a belt buckle made from chalcedony with fossilized Elimia tenera shells (formerly Goniobasis tenera and incorrectly Turritella) from the Eocene Green River Formation, Wyoming, USA. Belt buckle made and photograph taken by Thaddeus P. Bejnar, in the workshop of Waldemere Bejnar.
By Thaddeus P. Bejnar, Bejnar – Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=7003062