sedimentary
Chert (often referred to as Flint or Jasper)
Chalcedony (SiO2) - Silicon Dioxide
Hardness: 6.5–7 on Mohs scale; Color: typically tan, brown, or black as seen here; Luster: waxy to dull; Structure: microcrystalline/cryptocrystalline; Cleavage: none (fractures conchoidally); Specific Gravity: 2.65.
- Hardness
- 6
- Color
- typically tan, brown, or black as seen here
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: typically tan, brown, or black as seen here; Luster: waxy to dull; Structure: microcrystalline/cryptocrystalline; Cleavage: none (fractures conchoidally); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in sedimentary environments. It is often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads/knives) due to its sharp conchoidal fracture. Modernly used in construction aggregate, road surfacing, and as semi-precious gemstones (jasper/agate).
Geological facts
Because flint (a variety of chert) produces sparks when struck against steel, it was the primary ignition source for 'flintlock' firearms and early fire-starting tools for centuries.
Field identification & locations
Identify in the field by its distinctive 'shell-like' (conchoidal) fracture pattern and its ability to scratch glass. Commonly found in riverbeds, glacial tills, or embedded in limestone cliffs.
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