sedimentary
Chert
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 Mohs scale; Color: Brown, grey, tan with oxidation; Luster: Dull to waxy; Texture: Fine-grained/cryptocrystalline; Cleavage: None (conchoidal fracture)
- Hardness
- 7 Mohs scale
- Color
- Brown, grey, tan with oxidation
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 Mohs scale; Color: Brown, grey, tan with oxidation; Luster: Dull to waxy; Texture: Fine-grained/cryptocrystalline; Cleavage: None (conchoidal fracture)
Formation & geological history
Chemically precipitated from silica-rich fluids or through the accumulation of siliceous remains of microorganisms (like diatoms or radiolarians) within sedimentary layers. This weathered pebble-form suggests transport by water.
Uses & applications
Historically used for stone tools (arrowheads/knives) due to sharp edges; currently used for landscaping, road base, and as a collector's specimen for nature enthusiasts.
Geological facts
Chert is essentially the same as flint, though the name 'flint' is usually reserved for dark varieties found in chalk formations. It is very resistant to physical and chemical weathering.
Field identification & locations
Identify by its extreme hardness (will scratch glass) and smooth, curved (conchoidal) fracture surfaces. Commonly found in riverbeds, glacial till, and coastal deposits.
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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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