sedimentary
Chert (varieties include Jasper or Flint)
Chert (Microcrystalline Silica, formula: SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, grey, or yellowish-brown; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, grey, or yellowish-brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, grey, or yellowish-brown; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. This specimen appears weathered/water-worn, potentially from an ancient riverbed or beach deposit.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modernly used as road base, construction aggregate, and occasionally tumbled for lapidary jewelry.
Geological facts
Chert is so hard it can scratch steel. Because it breaks into very sharp edges, it was the primary material for survival tools during the Stone Age.
Field identification & locations
Identify in the field by its extreme hardness and 'conchoidal' (shell-like) fracture patterns. It won't react with acid and is commonly found in limestone or chalk beds globally.
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