sedimentary
Chert
Chert (SiO2)
Hardness: 7 Mohs scale; Color: typically gray, brown, or tan; Luster: dull to waxy; Crystal structure: cryptocrystalline (microscopic quartz); Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8.
- Hardness
- 7 Mohs scale
- Color
- typically gray, brown, or tan
- Luster
- dull to waxy
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Physical properties
Hardness: 7 Mohs scale; Color: typically gray, brown, or tan; Luster: dull to waxy; Crystal structure: cryptocrystalline (microscopic quartz); Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8.
Formation & geological history
Formed in marine or freshwater environments as a chemical precipitate or through the accumulation of siliceous biological microfossils like diatoms and radiolarians.
Uses & applications
Historically used for stone tools and weapons. Today used as road aggregate, architectural stone, and as a component in certain pottery and ceramics.
Geological facts
Flint is a variety of chert. It was one of the most important minerals for early humans because its conchoidal fracture creates extremely sharp edges for hunting tools.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy luster, and shell-like (conchoidal) fracture pattern. Found globally in limestone formations or as river gravel.
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Sandstone or Siltstone
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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