sedimentary

Chert Pebble

Chert (composed primarily of Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

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

Identified May 27, 2026More sedimentary →

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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.