sedimentary
Chert (Yellow Jasper variant)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Yellow-brown, tan, ochre; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.
- Hardness
- 6
- Color
- Yellow-brown, tan, ochre
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Yellow-brown, tan, ochre; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.
Formation & geological history
Formed through the accumulation of silica-rich fluids in sedimentary environments or by the replacement of carbonate rocks (limestone). Often found in nodules or bedded deposits within prehistoric marine sediments.
Uses & applications
Used historically for stone tools due to its sharp edges; modern uses include lapidary work (jewelry, cabochons), landscaping, and as a component in road construction.
Geological facts
Cultures worldwide used chert/flint for heat-treating to create extremely sharp arrowheads and blades. It can spark when struck against steel, which was essential for early fire-starting.
Field identification & locations
Identify by its waxy appearance, smooth conchoidal (shell-like) fracture, and its ability to scratch glass. Commonly found in riverbeds, gravel pits, and sedimentary outcrops.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
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Arenite (primarily SiO2)
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