sedimentary
Chert (Iron-stained)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Rusty brown, tan, or grey due to iron impurities; Luster: Dull to waxy; Structure: Microcrystalline with conchoidal (shell-like) fracture; Cleavage: None.
- Hardness
- 7 on Mohs scale
- Color
- Rusty brown, tan, or grey due to iron impurities
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Rusty brown, tan, or grey due to iron impurities; Luster: Dull to waxy; Structure: Microcrystalline with conchoidal (shell-like) fracture; Cleavage: None.
Formation & geological history
Formed from the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads). Modernly used as construction aggregate, road base, and occasionally for rock tumbling/landscaping.
Geological facts
Chert is extremely durable and chemically resistant. When it contains high amounts of iron oxide, it takes on the characteristic brownish-red 'jasper-like' appearance seen in this specimen.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, curved fracture surfaces. Commonly found in riverbeds, gravel pits, and glacial till.
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