sedimentary

Chert (often called Flint)

Microcrystalline to cryptocrystalline quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, gray; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 6
Color: Brown, tan, gray
Luster: Waxy to dull

Identified May 17, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, gray; 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 by precipitation from silica-rich groundwater replacing other minerals in limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its conchoidal fracture. Modernly used in construction aggregate and as a spark-generator in flint-and-steel fire starters.

Geological facts

This specimen appears to be a small flake of chert, which was the 'high-tech' material of the Stone Age. It breaks into sharp edges that can be even sharper than a surgical scalpel.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), its waxy feel, and the way it breaks into curved, shell-like shapes (conchoidal fracture). Commonly found in limestone outcrops or as river pebbles.