sedimentary
Chert (Gravel)
Chert (Microcrystalline Silicon Dioxide, SiO2)
Hardness: 7; Color: Tan, beige, white, and gray; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7
- Color
- Tan, beige, white, and gray
- Luster
- Dull to waxy
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Physical properties
Hardness: 7; Color: Tan, beige, white, and gray; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments. These specimens appear to be weathered fragments typically found in river beds or glacial till.
Uses & applications
Used primarily as construction aggregate, road base, and landscaping gravel. Historically used for stone tools due to its sharp edges when broken.
Geological facts
Chert is extremely durable and chemically resistant. It often contains micro-fossils of marine organisms that can only be seen under high magnification.
Field identification & locations
Look for a smooth, waxy texture and shell-like (conchoidal) fractures. Harder than glass and steel. Common in stream beds, gravel pits, and sedimentary rock outcrops globally.
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