sedimentary

Chert/Flint nodule or weathered river rock

Microcrystalline or cryptocrystalline silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, grey. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Brown, tan, grey
Luster: Waxy to dull

Identified August 25, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, grey. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through the diagenesis of silica-rich sediments or as nodules in limestone/chalk. Rounded shape indicates weathering and transport by water.

Uses & applications

Historically used for stone tools and starting fires. Currently used as gravel or for tumbling.

Geological facts

Chert and flint are essentially the same material, with 'flint' often referring specifically to chert found in chalk deposits.

Field identification & locations

Identified by its hardness (scratches glass), smooth waxy feel when polished or wet, and lack of visible crystals. Commonly found in riverbeds, beaches, and glacial till.