sedimentary
Chert (Flint Nodules)
Chert (Cryptocrystalline variety of Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, grey, or white with iron staining (orange/brown); Luster: Dull to waxy; Structure: Cryptocrystalline/microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, grey, or white with iron staining (orange/brown)
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, grey, or white with iron staining (orange/brown); Luster: Dull to waxy; Structure: Cryptocrystalline/microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of siliceous microfossils (like radiolaria or diatoms) or by chemical precipitation of silica in limestone or chalk beds. Often Cretaceous in age.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges when fractured. Today used in construction aggregate, road base, and as decorative gravel.
Geological facts
Chert is so hard it can scratch steel and glass. It was one of the first materials used by early humans to create fire because striking it against steel produces hot sparks.
Field identification & locations
Identify in the field by its waxy texture, extreme hardness, and 'shell-like' conchoidal fractures. Commonly found in stream beds or weathering out of limestone/chalk cliffs.
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