sedimentary

Chert (and/or River Pebble)

Microcrystalline silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, or buff; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, brown, or buff
Luster: Waxy to dull

Identified April 6, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, brown, or buff; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from groundwater within limestone or chalk beds. Often smooth from water erosion in riverbeds.

Uses & applications

Historically used for stone tools (arrowheads). Modernly used as gravel for construction, road base, and decorative landscaping.

Geological facts

Chert is remarkably durable and resistant to chemical weathering. Varieties with high iron content are often called jasper, while dark varieties are known as flint.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. It is commonly found in river deposits, gravel pits, and sedimentary rock outcrops.