sedimentary
Chert (Jasper-like Silicate)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, and dark grey banding; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, and dark grey banding
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, and dark grey banding; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich microfossils or precipitation from silica-rich fluids in sedimentary basins. Hardening occurs through deep burial and chemical alteration over millions of years.
Uses & applications
Used historically for stone tools and arrowheads due to its sharp edges; currently used for decorative purposes, landscape gravel, and as semi-precious lapidary material.
Geological facts
Chert is so hard it can strike sparks against steel. It is one of the most common materials used by early humans for lithic technology across the globe.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds or within limestone 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
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Sandstone
Arenite (primarily SiO2)
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