sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, brown with reddish iron staining; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, brown with reddish iron staining
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, brown with reddish iron staining; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments; generally hundreds of millions of years old
Uses & applications
Historically used for stone tools (arrowheads, scrapers); currently used as road aggregate and in some landscaping
Geological facts
Chert has a conchoidal fracture pattern similar to glass, which allows it to be knapped into extremely sharp edges. It is often found as nodules within limestone or shale beds.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like fracture surfaces. Often found in riverbeds or outcrops of sedimentary rock.
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Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Shale or Slaty Mudstone
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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