sedimentary
Chert (Jasper/Flint variety)
Microcrystalline quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Dark grey to brown with light banding, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Dark grey to brown with light banding, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. This specimen shows water-worn rounding, suggesting it was found in a river or beach deposit.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to sharp edges; currently used for lapidary work, jewelry, and construction aggregate.
Geological facts
Chert was one of the most important minerals for early humans because of its ability to fracture into extremely sharp blades. High-purity dark varieties are often called flint.
Field identification & locations
Identify in the field by its hardness (it should scratch glass), its smooth, waxy surface when damp, and its characteristic curved (conchoidal) fracture lines on broken surfaces.
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