sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Grey-brown to tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs scale
Color: Grey-brown to tan
Luster: Waxy to dull

Identified July 6, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Grey-brown to tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed by the accumulation of siliceous remains such as radiolarian tests or through chemical precipitation in carbonate environments. Often found as nodules or layers within limestone or chalk formations.

Uses & applications

Historically used for making stone tools due to its sharp edges; used currently as a construction aggregate, for landscaping, and as fire-starting flint.

Geological facts

Chert has been used by humans for hundreds of thousands of years to create arrowheads, scrapers, and knives. When struck against steel, it creates sparks used to ignite tinder.

Field identification & locations

Identified in the field by its hardness (scratches glass), waxy texture, and distinctive shell-like (conchoidal) fracture pattern when broken. Commonly found in riverbeds or within limestone outcrops.