sedimentary
Chert Pebble
Chert (composed primarily of Microcrystalline Quartz, SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, and gray mottled; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8
- Hardness
- 6
- Color
- Brown, tan, and gray mottled
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, and gray mottled; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within sedimentary rock layers such as limestone. Often found as rounded pebbles due to water erosion in riverbeds.
Uses & applications
Used historically for stone tools and strike-a-lights; currently used in construction aggregate, road surfacing, and as decorative river rock in landscaping.
Geological facts
Chert was one of the most important materials for prehistoric humans because it breaks with sharp, durable edges suitable for arrowheads and scrapers. Flint is a high-quality variety of chert.
Field identification & locations
Identify by its hardness (it will scratch glass) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in gravel pits, stream beds, and coastal areas throughout the world.
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