One intuitively chosen agate tumble. 
Size: 18-26mm (Range)
Type: Turritella Fossil Agate 
Age: 50 million years (Eocene)
Location: Green River Formation, Wyoming, USA
Turritella is a genus of medium-sized sea snails with an operculum, marine gastropod mollusks in the family Turritellidae. They have tightly coiled shells, whose overall shape is basically that of an elongated cone.