sedimentary
Chert (potentially Fossiliferous or Jasperoid)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, and brownish-yellow; Luster: Waxy to dull (earthy in weathered state); Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, and brownish-yellow
- Luster
- Waxy to dull (earthy in weathered state)
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, and brownish-yellow; Luster: Waxy to dull (earthy in weathered state); Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture).
Formation & geological history
Formed via the accumulation of silica-rich marine organisms (like radiolaria or diatoms) or by chemical precipitation in groundwater replacing limestone. This specimen appears water-worn, likely from a river or glacial deposit.
Uses & applications
Historically used for stone tools (flintknapping) due to its sharp edges; today used as aggregate in construction or as lapidary material if featuring attractive patterns.
Geological facts
Chert is so durable that it often survives long-distance transport in rivers and glaciers long after the surrounding rock has eroded. Some chert contains microscopic fossils of ancient marine life.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel knife) and waxy texture where freshly chipped. Common in riverbeds and limestone regions. Look for the characteristic conchoidal (shell-like) fracture patterns.
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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