sedimentary
Chert (Jasper/Flint variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, or light yellow-brown. Luster: Dull to waxy. Crystal Structure: Microcrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Tan, brown, or light yellow-brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, or light yellow-brown. Luster: Dull to waxy. Crystal Structure: Microcrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the chemical replacement of calcium carbonate in limestone by silica-rich fluids. Usually found in ancient sea beds or glacial deposits.
Uses & applications
Historically used for stone tools and weapons due to sharp fractures. Today, used in construction aggregate, road surfacing, and occasionally as decorative river stones.
Geological facts
Chert is incredibly durable and chemically stable, which is why it often survives as rounded pebbles in stream beds long after other rocks have eroded away. Native Americans used this specific material for projectile points.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds, gravel pits, and glacial till across North America.
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