sedimentary
Banded Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Tan, brown, and cream bands; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 7 Mohs scale
- Color
- Tan, brown, and cream bands
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Tan, brown, and cream bands; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Forms through the accumulation of silica-rich organic remains or chemical precipitation in marine or freshwater environments, dating from the Precambrian to recent periods.
Uses & applications
Used historically for stone tools due to its sharp edges when broken; currently used as aquarium gravel, decorative landscaping stones, and occasionally for lapidary art.
Geological facts
Chert is essentially a non-gemstone variety of jasper or agate. It is incredibly durable and resistant to chemical weathering.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and the presence of shell-like (conchoidal) fracture lines. Found globally in limestone and chalk beds.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Clastic Sedimentary Rock Grain (SiO2 dominated)
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