sedimentary
Chert (Nodule)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Light grey to tan. Luster: Dull to waxy. Structure: Non-crystalline mass (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
- Hardness
- 6
- Color
- Light grey to tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Light grey to tan. Luster: Dull to waxy. Structure: Non-crystalline mass (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
Formation & geological history
Formed through the replacement of limestone or carbonate material by silica-rich fluids in marine environments. This specimen appears to be a stream-tumbled waterworn nodule, likely dating from the Paleozoic or Mesozoic eras depending on the local bedrock.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in construction aggregate, road surfacing, and as a raw material for high-silica industrial applications.
Geological facts
Chert is so hard it can strike sparks against steel. Because of its microscopic crystal structure, it breaks like glass, making it the primary material for prehistoric 'flint knapping' across many cultures.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel nail), its smooth 'waxy' texture when broken, and its rounded, weathered exterior. Commonly found in riverbeds and limestone outcrops globally.
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