sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed as nodules or beds in sedimentary rocks (like limestone) through the accumulation of silica-rich organic remains or chemical precipitation. Primarily found in Phanerozoic strata.
Uses & applications
Historically used for stone tools and starting fires (striking steel). Modernly used in road construction, and higher quality varieties are used for jewelry and lapidary art.
Geological facts
Chert has a conchoidal fracture, similar to glass, which allows it to be broken into extremely sharp edges. It was the primary material for arrowheads and scrapers for thousands of years.
Field identification & locations
Identify in the field by its waxy texture and shell-like (conchoidal) fracture pattern when broken. It will easily scratch glass and cannot be scratched by a steel knife.
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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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