sedimentary
Chert (Banded)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: tan, grey, brown with banded layers, Luster: waxy to dull, Structure: cryptocrystalline, Fracture: conchoidal
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: tan, grey, brown with banded layers, Luster: waxy to dull, Structure: cryptocrystalline, Fracture: conchoidal
Formation & geological history
Formed by the accumulation of siliceous remains of organisms (radiolarians/diatoms) or chemical precipitation from silica-rich groundwater within limestone or chalk beds.
Uses & applications
Used historically for stone tools and arrowheads; currently used as road aggregate, in jewelry as semi-precious stones, and as a decorative landscaping rock.
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 produces extremely sharp edges.
Field identification & locations
Identify by its hardness (cannot be scratched by a knife), waxy appearance, and layered or banded patterns. Commonly found in riverbeds, gravel pits, and sedimentary outcrops.
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Brecciated Chert (Microcrystalline Silica)
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