sedimentary
Chert (Flint nodule)
Silicon dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, gray, or white exterior with a waxy, translucent gray interior; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, gray, or white exterior with a waxy, translucent gray interior; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the replacement of limestone or chalk by silica-rich fluids, often accumulating as nodules or lenses within carbonate rock layers during the diagenesis process, frequently in ancient marine environments.
Uses & applications
Historically used for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as a semi-precious stone for jewelry (Jasper/Agate variants).
Geological facts
Flint was the most important material for early human technology (Stone Age) because of its predictable conchoidal fracturing, which creates razor-sharp edges.
Field identification & locations
Identify by its extreme hardness (scratches glass), waxy inner texture when broken, and sharp, shell-like fracture patterns. Commonly found in chalk or limestone outcrops and riverbeds.
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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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Shale or Slaty Mudstone
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Arenite (primarily SiO2)
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