sedimentary
Brown Chert (Jasper-like)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Brownish-red to earthy tan, 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: Brownish-red to earthy tan, 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 microfossils or precipitation from hydrothermal fluids in sedimentary basins. The brown color comes from iron oxide (limonite or goethite) inclusions.
Uses & applications
Used as garden landscape stone, in flintknapping (historically for tools), and occasionally tumbled for jewelry or aquariums.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture allows it to be shaped into razor-sharp blades, arrowheads, and scrapers.
Field identification & locations
Identify in the field by its smooth, waxy surface when wet and its tendency to break with curved, glass-like edges. Commonly found in riverbeds, glacial tills, and limestone outcroppings.
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