sedimentary

Chert (River Pebble)

Microcrystalline Silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Tan, brown, or ochre; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Hardness: 6
Color: Tan, brown, or ochre
Luster: Waxy to dull

Identified July 8, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Tan, brown, or ochre; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments, later rounded and smoothed by water transport in a river or stream.

Uses & applications

Historical use for tool making (flint knapping), modern use as aggregate, decorative landscaping stone, or tumbled for collection.

Geological facts

Chert is chemically the same as quartz but lacks visible crystals. Because it breaks with a sharp edge, it was one of the primary materials used by prehistoric humans to create arrowheads and scrapers.

Field identification & locations

Identify in the field by its waxy texture, smooth water-worn surface, and ability to scratch glass. It often shows 'crescent' impact marks from hitting other rocks in rivers.