sedimentary

Chert (River Stone)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: Gray, brown, tan, and waxy; Luster: Dull to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs scale
Color: Gray, brown, tan, and waxy
Luster: Dull to waxy

Identified July 1, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Gray, brown, tan, and waxy; Luster: Dull to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed via the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater. This specimen has been rounded and smoothed by water erosion in a river or beach environment.

Uses & applications

Historically used for stone tools (arrowheads). Currently used in decorative landscaping, construction aggregate, and as a polishing material for rock tumblers.

Geological facts

Chert and its variant, Flint, were among the first materials used by early humans to create fire and sharp tools due to their predictable conchoidal fracturing.

Field identification & locations

Identify in the field by its smooth, waxy feel, extreme hardness (it will scratch glass), and rounded 'river rock' shape. Found globally in riverbeds and sedimentary basins.