sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Silica (SiO2)
Hardness: 7 (Mohs scale), Color: Brown, tan, reddish-brown. Luster: Dull to waxy. Structure: Cryptocrystalline. Fracture: Conchoidal. Cleavage: None.
- Hardness
- 7 (Mohs scale), Color: Brown, tan, reddish-brown
- Color
- Brown, tan, reddish-brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown, tan, reddish-brown. Luster: Dull to waxy. Structure: Cryptocrystalline. Fracture: Conchoidal. Cleavage: None.
Formation & geological history
Formed by the precipitation of silica from groundwater within limestone or chalk beds, or from the accumulation of siliceous remains of marine organisms (diatoms/radiolarians).
Uses & applications
Historically used for making stone tools (arrowheads). Currently used for landscaping, as a construction aggregate, and occasionally for lapidary work if colorful.
Geological facts
Chert is so hard it will scratch steel. Archaeological sites often feature chert tools because of the sharp edges produced when fractured.
Field identification & locations
Identify by its waxy luster, smooth curved fracture surfaces, and extreme hardness. It is commonly found in sedimentary basins worldwide.
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