sedimentary

Chert (Gravel)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs); Color: Gray, tan, white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs)
Color: Gray, tan, white
Luster: Waxy to dull

Identified April 5, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs); Color: Gray, tan, white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. This specimen is a weathered piece of gravel found in concrete or aggregate.

Uses & applications

Used primarily in construction as aggregate for concrete and roadbeds. Historically used for making stone tools due to its sharp conchoidal fracture.

Geological facts

Chert is so hard it can strike sparks against steel. It is one of the most common materials used by prehistoric humans for arrowheads and scrapers.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy appearance, and smooth, curved (conchoidal) breaks. Often found in riverbeds or as component gravel in landscaping and driveways.