sedimentary
Chert (Nodular)
Microcrystalline Silica (SiO2)
Hardness: 7 on Mohs scale; Color: Pinkish-tan to light brown with white weathering rind; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Pinkish-tan to light brown with white weathering rind
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Pinkish-tan to light brown with white weathering rind; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of siliceous remains of organisms or chemical precipitation of silica in groundwater within sedimentary host rock (likely limestone or dolomite), typically in ancient marine environments.
Uses & applications
Historically used for stone tools (knapping) due to sharp edges; currently used for road base, aggregate, and occasionally as lapidary material for hobbyists.
Geological facts
Chert was one of the first materials used by early humans to create arrowheads and scrapers. Flint is a variety of chert. This specific specimen shows a 'caliche' or weathered exterior common in arid environments.
Field identification & locations
Identify by its hardness (it will scratch glass) and lack of visible grains. It often features smooth, curved (conchoidal) fractures when broken. Commonly found in desert regions where limestone has eroded away.
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