sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Dark gray to brownish with white quartz veining, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark gray to brownish with white quartz veining, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
Formation & geological history
Formation occurs when silica-rich fluids permeate sedimentary layers or through the accumulation of siliceous remains of organisms like diatoms and radiolarians; often found in limestone or dolomite beds.
Uses & applications
Historically used for flintknapping tools; currently used as construction aggregate, in road decorative landscaping, or as tumbled stones for hobbyists.
Geological facts
Because it fractures conchoidally like glass, chert (often called flint) was the primary material for prehistoric arrowheads, scrapers, and fire-starting kits throughout human history.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and waxy, smooth texture. Look for smooth, shell-like curves on broken surfaces. Common in riverbeds and limestone outcrops.
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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