Turritella Agate (Fossiliferous Chert)

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, cream, and black; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.60-2.65.

Formation & Geological History

Formed during the Eocene Epoch (approx. 50 million years ago) in freshwater lakes. This is a silicified fossiliferous stone where the spiral shells of freshwater snails (Elimia tenera) were replaced by chalcedony/agate.

Uses & Applications

Used primarily for lapidary work, jewelry (cabochons), interior decoration items (like the bowl shown), and as collectible fossil specimens.

Geological Facts

Despite its common name 'Turritella Agate,' the fossils are actually freshwater snail shells of the genus Elimia, not the marine snail Turritella. It is the official state fossil of Wyoming.

Field Identification & Locations

Identify by the distinctive spiral-shaped snail shells embedded in a dark or light silicate matrix. It is famously found in the Green River Formation in Wyoming, USA. Collectors look for high contrast between the fossils and the surrounding stone.

Identified on: 4/29/2026

Mode: Standard