sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5–7 (Mohs scale); Color: Brown, grey, tan with mottling; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
- Hardness
- 6
- Color
- Brown, grey, tan with mottling
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 (Mohs scale); Color: Brown, grey, tan with mottling; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments; commonly found in nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to sharp edges; currently used for road surfacing, jewelry (when colorful), and river rock landscaping.
Geological facts
Chert has a conchoidal fracture, meaning it breaks like glass to create razor-sharp edges. It was one of the most important raw materials for early humans to create survival tools.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its smooth 'waxy' texture when broken, and the lack of visible grains. Commonly found in riverbeds and glacial tills.
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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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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Shale or Slaty Mudstone
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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