sedimentary

Chert Pebble (Flint)

Microcrystalline/Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Gray to olive with white inclusions; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Gray to olive with white inclusions
Luster: Waxy to dull

Identified March 9, 2026More sedimentary →

Explore Chert Pebble (Flint) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 7 (Mohs scale); Color: Gray to olive with white inclusions; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the precipitation of silica from seawater or the accumulation of silica-rich organic debris (like radiolarians or diatoms) within sedimentary beds. This specimen has been rounded by fluvial (river) or coastal erosion during the Holocene epoch.

Uses & applications

Historically used for making stone tools (arrowheads). Modern uses include road ballast, decorative landscaping gravel, and as a raw material for fire-starting in survival kits.

Geological facts

When struck against steel, chert produces sparks, making it essential for flintlock firearms and early fire-making. It is one of the most durable common rocks, often surviving long-distance transport in rivers and along shorelines.

Field identification & locations

Identify in the field by its hardness (will scratch glass), smooth texture, and white weathered 'cortex' or patches. Commonly found in riverbeds, glacial tills, and beaches worldwide. This specific specimen shows characteristic rounding and impact scars from water transport.