sedimentary

Chert (Flint)

Chert (Cryptocrystalline Silicon Dioxide, SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Hardness: 6
Color: Brown, tan, or grey
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Formation & geological history

Formed in marine environments through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation. Occurs as nodules or bedded deposits within limestone or chalk.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to its sharp edges. Modernly used in construction aggregate and as a spark-generating material in survival gear.

Geological facts

Chert has been used by humans for over 2 million years. When struck against steel, it produces sparks, making it essential for early fire-starting and flintlock firearms.

Field identification & locations

Identify by its smooth, waxy feel and shell-like (conchoidal) fractures. It is commonly found in gravel beds or weathering out of limestone cliffs. Often found as rounded pebbles on beaches.