sedimentary
Chert (Nodule)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Tan, brown, or beige; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Fracture: Conchoidal; Specific gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Tan, brown, or beige
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Tan, brown, or beige; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Fracture: Conchoidal; Specific gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich microfossils or groundwater precipitation within limestone or chalk beds, often from the Cretaceous period
Uses & applications
Widely used for stone tools (arrowheads) in prehistory; currently used as road aggregate and for lapidary tumbling
Geological facts
Chert nodules are often called 'flint' when found in chalk. It was one of the first materials used by early humans for tool-making due to its predictable fracture patterns
Field identification & locations
Identified by its extreme hardness (scratches glass), smooth waxy feel, and sharp edges when broken. Commonly found in riverbeds and limestone outcrops
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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