sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Tan, beige, or gray; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Tan, beige, or gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Tan, beige, or gray; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed by the accumulation of silica-rich microfossils or chemical precipitation from silica-rich fluids in sedimentary basins. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) and starting fires. Currently used in road construction, as an abrasive, and occasionally for lapidary work.
Geological facts
Chert has a conchoidal fracture, which allows it to break into sharp edges, making it the primary material for prehistoric survival tools and weapons.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy feel, and sharp, curved edges when broken. Found globally in limestone layers.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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