sedimentary

Chert (Flint Nodules)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, white, and grey; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, brown, white, and grey
Luster: Dull to waxy

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, brown, white, and grey; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges when broken. Today used as road surfacing, decorative gravel, and for start-striking (fire starting).

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it produces sparks, which is why it was the primary material for flintlock firearms and early fire-making kits.

Field identification & locations

Identify in the field by its smooth, waxy texture and shell-like (conchoidal) breaks. It is very common in riverbeds and limestone outcrops globally. Look for a white 'cortex' or weathered outer layer.