fossil

Fossilized Gryphaea (Devil's Toenail)

Gryphaea arcuata (Bivalvia: Gryphaeidae)

AI-generated identification · may be incorrect

Hardness: 3-4 (calcite); Color: Rusty brown, tan, or grey; Luster: Dull or earthy; Structure: Thick, coiled or recurved calcitic shell with distinct growth lines; Specific Gravity: ~2.7

Hardness: 3-4 (calcite)
Color: Rusty brown, tan, or grey
Luster: Dull or earthy

Identified July 2, 2026More fossil →

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Physical properties

Hardness: 3-4 (calcite); Color: Rusty brown, tan, or grey; Luster: Dull or earthy; Structure: Thick, coiled or recurved calcitic shell with distinct growth lines; Specific Gravity: ~2.7

Formation & geological history

Formed during the Jurassic and Cretaceous periods (approx. 200-66 million years ago) in shallow, muddy marine habitats where these extinct oysters lived in large colonies.

Uses & applications

Primarily for educational purposes, paleontological research, and as a popular item for amateur fossil collectors and children.

Geological facts

Gryphaea are often called Devil's Toenails due to their unique curved shape. They are famous examples of rapid evolution in the fossil record, showing a lineage that became increasingly coiled over time.

Field identification & locations

Identified by its distinctive curved, horn-like shape and thick, ribbed shell. Commonly found in Mesozoic limestone and clay deposits globally, especially in Europe and North America. Use vinegar to test for calcite (fizzing).