sedimentary
Chert Pebble
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Gray to olive-brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Gray to olive-brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray to olive-brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic debris (like radiolaria or diatoms) or chemical precipitation in marine environments; age varies by geological deposit.
Uses & applications
Historically used for stone tools (arrowheads); currently used as construction aggregate, road base, and common decorative landscaping stone.
Geological facts
Because it fractures conchoidally like glass, chert was one of the most important materials for early human technology. Flint is a specific variety of chert.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy luster when broken, and roundness caused by water erosion if found in a river or beach setting.
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