sedimentary
Chert (and Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, white, and rusty orange; Luster: Dull to waxy; Structure: Cryptocrystalline; Fracture: Conchoidal (smooth, curved breaks); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, white, and rusty orange
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, white, and rusty orange; Luster: Dull to waxy; Structure: Cryptocrystalline; Fracture: Conchoidal (smooth, curved breaks); Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or via chemical precipitation from silica-rich fluids within sedimentary rock layers, often limestone or dolomite.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used as road aggregate, landscaping stone, and occasionally in lapidary work for jewelry if colorful.
Geological facts
Chert is so durable that it often remains as 'float' long after the surrounding limestone bedrock has weathered away. It was one of the most important minerals for early human survival.
Field identification & locations
Identify by its high hardness (it will scratch glass or steel), smooth waxy feel on fresh surfaces, and circular 'conchoidal' fracture patterns. Common in riverbeds and limestone outcrops.
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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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