sedimentary
Chert (Quartz-rich)
Microcrystalline Silica (SiO2)
Hardness: 7 (Mohs scale), Color: Tan, brown, and cream with slight iron staining. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: Approximately 2.6.
- Color
- Tan, brown, and cream with slight iron staining
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale), Color: Tan, brown, and cream with slight iron staining. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: Approximately 2.6.
Formation & geological history
Formed through the accumulation of silica-rich micro-organisms or chemical precipitation in marine environments. Often found as nodules in limestone or dolomite. Geologically common from Pre-Cambrian to present.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges. Currently used in road aggregate, aquarium decor, and occasionally as high-quality lapidary material.
Geological facts
Chert was one of the most important minerals for early humans, used to create arrowheads, scrapers, and fire-starting tools. It is highly resistant to chemical weathering.
Field identification & locations
Identify in the field by its superior hardness (scratches glass) and shell-like (conchoidal) fracture pattern when broken. It often feels denser and smoother than surrounding limestone.
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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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