sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Gray, tan, brown with iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Hardness: 7 (Mohs scale)
Color: Gray, tan, brown with iron staining
Luster: Waxy to dull

Identified June 20, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Gray, tan, brown with iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Formation & geological history

Forms primarily through the accumulation of silica-rich organic remains or chemical precipitation within limestone or chalk beds. It can date from almost any geological era where marine sediments were deposited.

Uses & applications

Historically used for stone tools and weapons (arrowheads). Modernly used in road construction as aggregate and occasionally as a flux in glassmaking or as gemstone specimens for collectors.

Geological facts

Chert has a distinctive conchoidal fracture, creating sharp edges which is why it was the primary material for prehistoric tools. When struck against steel, it can produce sparks of fire.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy texture, and shell-like (conchoidal) breaking pattern. Commonly found as nodules in limestone regions.