sedimentary
Chert (variations include Flint)
Silicon Dioxide (SiO2)
Hardness: 7 Mohs; Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 Mohs
- Color
- Gray, tan, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed by the precipitation of silica from water, often replacing organic material or filling cavities in limestone/dolomite. Common in marine sedimentary environments through various geological ages.
Uses & applications
Used historically for stone tools and reaching fire (flint). Currently used as a raw material for ceramics, construction aggregate, and occasionally for lapidary work.
Geological facts
Chert was one of the most vital resources for prehistoric humans due to its ability to be chipped into sharp edges. It is extremely resistant to chemical weathering.
Field identification & locations
Identify by its waxy appearance and the sharp, curved (conchoidal) edges when broken. It will easily scratch glass and steel. Found globally in nodules or bedded layers within limestone.
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Arenite (if sandstone)
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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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