sedimentary

Chert Pebble

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs; Color: Gray, brown, or dull beige; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs
Color: Gray, brown, or dull beige
Luster: Waxy to dull

Identified July 17, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Gray, brown, or dull beige; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); 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 in marine environments. Often found as nodules within limestone or as water-worn pebbles.

Uses & applications

Historically used for stone tools due to sharp edges when fractured; modernly used as road aggregate, in landscaping, or as garden stones.

Geological facts

Chert was a primary material for prehistoric arrowheads and scrapers. When struck against steel, it can produce sparks, though it is less famous for this than its variety, flint.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel blade) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds and coastal areas.