sedimentary
Chert (Iron-stained)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Brownish-tan with iron staining, Luster: Waxy to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Brownish-tan with iron staining, Luster: Waxy to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments. The specimen shows smooth edges indicating water-worn weathering.
Uses & applications
Historically used for stone tools/arrowheads due to conchoidal fracture which creates sharp edges. Currently used as road aggregate, in concrete, and occasionally as a landscape rock.
Geological facts
Chert is extremely durable and chemically stable, often surviving millions of years of erosion that wears away other stones. The brown hue is typically caused by iron oxide impurities.
Field identification & locations
Identify in the field by its smooth, waxy texture and shell-like (conchoidal) fractures. It will easily scratch glass but cannot be scratched by a steel knife. Common in riverbeds and gravel pits.
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