sedimentary

Chert (Flint Pebbles)

Microcrystalline quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, beige, or gray with a dull to waxy luster; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Hardness: 7 on Mohs scale
Color: Tan, beige, or gray with a dull to waxy luster

Identified May 16, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, beige, or gray with a dull to waxy luster; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed as nodules in limestone or chalk beds from the precipitation of silica. This specific specimen shows signs of alluvial weathering and water-tumbling, likely from a river or beach environment.

Uses & applications

Historically used for making stone tools and fire-starting; currently used in construction aggregate, road surfacing, and as landscaping gravel.

Geological facts

Chert is so hard it can scratch glass and steel. It was one of the most important minerals for early humans because its conchoidal fracture creates extremely sharp edges for hunting and scraping.

Field identification & locations

Identify in the field by its smooth, rounded shape (if water-worn), extreme hardness, and distinctive shell-like (conchoidal) fracture pattern if broken. Commonly found in riverbeds and coastal areas.