sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, brown, white, and grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6
- Hardness
- 7 (Mohs scale)
- Color
- Tan, brown, white, and grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, brown, white, and grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6
Formation & geological history
Formed in marine environments through the accumulation of silica-rich microfossils or chemical precipitation within limestone or chalk beds. Most specimens date from the Paleozoic or Mesozoic eras.
Uses & applications
Historically used for stone tools and weapons (arrowheads/scrapers) due to its sharp fracture edges. Today used in some construction aggregates and for striking sparks in survival kits.
Geological facts
Chert has been used by humans for over 2 million years. When struck against steel, it creates sparks, which led to the development of flintlock firearms.
Field identification & locations
Identify by its characteristic seashell-like (conchoidal) fracture pattern and its ability to scratch glass. Commonly found as nodules in sedimentary rock layers or as pebbles in riverbeds.
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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
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Sandstone
Arenite (primarily SiO2)
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