sedimentary
Chert (varietal Flint)
Microcrystalline quartz (SiO2)
Hardness: 7 Mohs; Color: Brown, tan, and dark grey/black; Luster: Vitreous to waxy; Structure: Cryptocrystalline; Cleavage: Conchoidal fracture; SG: 2.65
- Hardness
- 7 Mohs
- Color
- Brown, tan, and dark grey/black
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 Mohs; Color: Brown, tan, and dark grey/black; Luster: Vitreous to waxy; Structure: Cryptocrystalline; Cleavage: Conchoidal fracture; SG: 2.65
Formation & geological history
Chemical precipitation from silica-rich fluids within sedimentary rock layers, often limestone or chalk. Commonly formed during the Paleozoic or Mesozoic eras in marine environments.
Uses & applications
Historical toolmaking (arrowheads, scrapers), primitive fire-starting, modern jewelry (cabs), and decorative landscaping stone.
Geological facts
Flint was crucial to human development; its ability to produce sparks when struck against steel and its razor-sharp conchoidal fracture edges made it the premier material for tools and weapons for millennia.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture, extreme hardness (scratches glass), and waxy texture. Often found as nodules within limestone or as river-worn pebbles.
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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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Clastic Sedimentary Rock Grain (SiO2 dominated)
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