sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Brown, tan, and grey, Luster: Waxy to dull, Crystal 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: Brown, tan, and grey, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments; commonly found in limestone or chalk beds. Most specimens date from the Paleozoic to Mesozoic eras.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to conchoidal fracturing. Modernly used in landscaping, as a construction aggregate, and occasionally for lapidary work.
Geological facts
Chert is so hard it can strike sparks against steel, which led to its use in 'flintlock' firearms. It is incredibly chemically stable and can survive millions of years of erosion.
Field identification & locations
Identify by its waxy luster, edge sharpness when broken, and inability to be scratched by a steel knife. Commonly found in riverbeds, gravel pits, and eroded cliff faces.
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