sedimentary

Chert (Field Stone)

Chert (Silicon Dioxide, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Dull tan to grey with brownish staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Dull tan to grey with brownish staining
Luster: Waxy to dull

Identified March 29, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Dull tan to grey with brownish staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine or groundwater environments. This specimen appears weathered/water-worn.

Uses & applications

Historical use for stone tools and arrowheads; modern use in road gravel, decorative landscaping, and as a source of silica in glass manufacturing.

Geological facts

Chert is so hard it can create sparks when struck against steel. Due to its predictable fracture pattern, it was the primary material for prehistoric 'flint-knapping' tools.

Field identification & locations

Identify in the field by its superior hardness (cannot be scratched by a steel blade) and smooth, shell-like (conchoidal) breaks. Very common in riverbeds and limestone outcrops.