sedimentary
Chert (specifically Flint or Jasper variant)
Microcrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, and dark gray; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, and dark gray
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, and dark gray; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich fluids in sedimentary environments, often replacing carbonate material or precipitating from groundwater. Common in limestone and chalk beds.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges; used today as decorative stones, in construction aggregate, and occasionally in lapidary work.
Geological facts
Chert (or flint) was one of the most important minerals for early humans, used to create fire and sharp projectiles. It can contain microfossils of diatoms or radiolarians.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture and high hardness (it will scratch glass). Often found in riverbeds or as nodules within limestone outcrops.
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Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
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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