sedimentary
Chert (Flint)
Silicon dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: tan, brown, gray, black, Luster: waxy to dull, Crystal structure: microcrystalline/cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.5-2.8
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: tan, brown, gray, black, Luster: waxy to dull, Crystal structure: microcrystalline/cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.5-2.8
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires; currently used as a road aggregate, in jewelry (agate varieties), and for scientific research into ancient environments.
Geological facts
Crystalline silica replaces organic matter or carbonate minerals. Because it breaks with a conchoidal fracture like glass, it was the primary material for arrowheads and scrapers in the Stone Age.
Field identification & locations
Look for a smooth, waxy texture and sharp, curved edges where broken. It is harder than steel and will scratch glass. Found globally in coastal cliffs or gravel pits.
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