sedimentary
Chert (within Asphalt)
Chert (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, beige, brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Tan, beige, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, beige, brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine or groundwater environments. These specimens are often sourced from river gravels or quarries as aggregate for road construction.
Uses & applications
Used primarily as aggregate in construction, road surfaces (asphalt), and concrete. Historically used for stone tools (arrowheads) due to its sharp conchoidal fracture.
Geological facts
Chert is so hard it can create sparks when struck against steel. Flint is a well-known dark variety of chert. This specific piece is acting as 'aggregate' in a bituminous pavement mixture.
Field identification & locations
Identify by its 'flint-like' waxy texture, smooth curved (conchoidal) breaks, and the fact that it cannot be scratched by a steel knife. Common in limestone regions and as creek bed gravel.
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