sedimentary
Chert / Flint Pebble with Fossil Cavity
Silicon Dioxide (SiO2)
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
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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.
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