sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Brown, tan, and grey with possible waxy luster; Crystal Structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Brown, tan, and grey with possible waxy luster

Identified March 15, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Brown, tan, and grey with possible waxy luster; Crystal Structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed via the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Often found in Phanerozoic age strata.

Uses & applications

Historically used for stone tools (arrowheads). Modern uses include road surfacing, jewelry (as jasper/agate variants), and as a sparking agent in survival gear.

Geological facts

Chert possesses a conchoidal fracture, which means it breaks like glass, creating razor-sharp edges. This property made it the primary material for the Stone Age technology revolution.

Field identification & locations

Identify by its 'waxy' appearance, extreme hardness (it will scratch glass), and the way it chips into bowl-shaped (conchoidal) flakes. Common in gravel pits, riverbeds, and limestone outcrops.