sedimentary
Chert (Chert / Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on the Mohs scale. Color: Tan, grey, brown, or variegated (as seen in the specimen). Luster: Dull to waxy. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Tan, grey, brown, or variegated (as seen in the specimen)
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on the Mohs scale. Color: Tan, grey, brown, or variegated (as seen in the specimen). Luster: Dull to waxy. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by the chemical precipitation of silica in groundwater. Often found as nodules within limestone or chalk beds. Geological age can range from Precambrian to Holocene.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Currently used as a road aggregate, in abrasive manufacturing, and as a decorative stone for lapidary work.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture allows it to be 'knapped' into extremely sharp blades. High-quality varieties like Flint were essential for early firearms (flintlocks).
Field identification & locations
Identify in the field by its hardness (will easily scratch glass) and its curved, shell-like (conchoidal) fracture surfaces. Commonly found in outcroppings of sedimentary rock like limestone. Tips for collectors: look for 'nodules' that feel heavier than the surrounding rock.
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