sedimentary
Chert (Flint / Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale. Color: Brownish-tan to caramel-yellow. Luster: Waxy to dull. Fracture: Pronounced conchoidal fracture with sharp edges. Structure: Cryptocrystalline. Cleavage: None.
- Hardness
- 7 on Mohs scale
- Color
- Brownish-tan to caramel-yellow
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: Brownish-tan to caramel-yellow. Luster: Waxy to dull. Fracture: Pronounced conchoidal fracture with sharp edges. Structure: Cryptocrystalline. Cleavage: None.
Formation & geological history
Formed biogenically or chemically through the precipitation of silica in marine or lacustrine sedimentary environments, often replacing carbonate rocks like limestone or chalk.
Uses & applications
Historically used for making sharp stone tools (arrowheads, scrapers) and spark-striking flints. Modern uses include lapidary, knapping, decorative stones, and aggregate.
Geological facts
Chert has been used by humans for over two million years to craft sharp tools. When struck against iron or pyrite, fine particles produce hot sparks that ignite tinder.
Field identification & locations
Identified by its high hardness (scratches glass), distinct smooth conchoidal fracture edges, and waxy luster. Widely found in gravel beds, chalk cliffs, and limestone formations globally.
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