sedimentary
Chert (Nodular Chert)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Tan, brown, or ochre; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Tan, brown, or ochre
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 Mohs scale; Color: Tan, brown, or ochre; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed by the accumulation and lithification of silica-rich materials, typically in marine environments where silica replaces carbonate minerals or precipitates from groundwater. Common in limestone and dolostone formations.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its conchoidal fracture. Today used as road base, construction aggregate, and occasionally for lapidary work.
Geological facts
Chert is essentially the same chemical composition as flint and Jasper; the names are often used interchangeably depending on color and regional preference. It is chemically very stable and resistant to weathering.
Field identification & locations
Identify in the field by its superior hardness (cannot be scratched by steel) and curved, glass-like fracture surfaces. Often found as rounded nodules or distinct layers within softer limestone cliffs.
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Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Shale or Slaty Mudstone
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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