sedimentary

Chert / Flint Pebble with Fossil Cavity

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, tan, or white
Luster: Dull to waxy

Identified July 14, 2026More sedimentary →

Explore Chert / Flint Pebble with Fossil Cavity in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed as a chemical precipitate in shallow marine environments, often replacing calcium carbonate. This specimen likely contains a mold or cast of a small marine invertebrate fossil, such as a bryozoan or coral, which has partially eroded away.

Uses & applications

Primarily of interest to rockhounds and beachcombers. Historically used for stone tools due to sharp edges upon fracturing.

Geological facts

The hole in this stone is a natural fossil mold. When marine organisms are trapped in silica-rich sediment, their shells may dissolve over millions of years, leaving behind a perfectly shaped cavity in the hardened rock.

Field identification & locations

Identify by its waxy texture, extreme hardness (will scratch glass), and rounded water-worn exterior. Commonly found on beaches or in gravel pits in areas with limestone bedrock.