sedimentary
Chert (with Iron Staining)
Silicon Dioxide (SiO2 / Cryptocrystalline Quartz)
Hardness: 7 (Mohs scale), Color: tan to reddish-brown (from iron oxidation) with gray core, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to reddish-brown (from iron oxidation) with gray core, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine or groundwater environments. This specimen shows a weathered exterior with iron-oxide staining.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Modernly used as road aggregate or in jewelry (as flint or jasper variant).
Geological facts
Chert is so hard it can strike sparks against steel, a property that led to its use in flintlock firearms. It is incredibly chemically stable and can survive for millions of years in soil.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel knife. Commonly found in limestone beds as nodules or layers. Look for a smooth, waxy texture on fresh breaks.
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