sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: reddish-brown, tan, and grey banding; Luster: dull to waxy; Structure: cryptocrystalline; Breakage: conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Color
- reddish-brown, tan, and grey banding
- Luster
- dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: reddish-brown, tan, and grey banding; Luster: dull to waxy; Structure: cryptocrystalline; Breakage: conchoidal fracture.
Formation & geological history
Formed via the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in sedimentary environments. Common in limestone and chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used as decorative stone, in lapidary work, and as a component in road construction.
Geological facts
Chert has been used by humans for over 2 million years. Its ability to produce sparks when struck against steel made it essential for flintlock firearms and fire-starting.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found as nodules or layers within sedimentary rock formations.
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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