sedimentary
Chert (Jasper/Flint variant)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs); Color: Tan, beige, brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs)
- Color
- Tan, beige, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs); Color: Tan, beige, brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments; often occurs as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads/knives) due to its sharp conchoidal edges; currently used in construction aggregate and as a collector's specimen.
Geological facts
Chert was one of the most important minerals for early humans because its predictable fracturing allowed for the creation of precise, razor-sharp tools and weapons.
Field identification & locations
Identify by its extreme hardness (scratches glass), waxy texture, and shell-like (conchoidal) fracture pattern. Commonly found in riverbeds or eroding out of limestone cliffs.
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Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
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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