sedimentary
Chert (Yellow Jasper/Flint)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Yellow-brown to tan with ochre weathering; Luster: Dull to waxy; Structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Yellow-brown to tan with ochre weathering
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Yellow-brown to tan with ochre weathering; Luster: Dull to waxy; Structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical replacement of limestone/dolomite by silica-rich fluids. Often found in nodules within sedimentary host rocks.
Uses & applications
Historically used for making stone tools (arrowheads). Modernly used in landscaping, as a gemstone (Jasper), and as a component in construction aggregate.
Geological facts
Chert is so hard that it can strike sparks from steel, which led to its use in flintlock firearms. It is chemically identical to quartz but has a different, microscopic crystal structure.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture and its ability to scratch glass. It is commonly found in riverbeds and as landscape gravel in North America and Europe.
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