sedimentary
Chert/Flint nodule or weathered river rock
Microcrystalline or cryptocrystalline silica (SiO2)
AI-generated identification · may be incorrectHardness: 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
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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.
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