sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: tan, grey, and brown; Luster: waxy to dull; Structure: microcrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- tan, grey, and brown
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, grey, and brown; Luster: waxy to dull; Structure: microcrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Often Cretaceous in age.
Uses & applications
Historically used for stone tools and starting fires; currently used in construction aggregate and as decorative landscaping stones.
Geological facts
Because it breaks with a conchoidal (shell-like) fracture, it creates razor-sharp edges which is why it was the primary material for arrowheads and knives for millennia.
Field identification & locations
Identify by its extreme hardness (scratches glass), waxy feel, and smooth curved surfaces where it has chipped. Common in riverbeds and limestone outcrops worldwide.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Sandstone
Arenite (primarily SiO2)
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