sedimentary

Chert (Flinty variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Grey to dark grey with waxy luster; Crystal structure: Trigonal (microscopic); Fracture: Conchoidal; Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Grey to dark grey with waxy luster

Identified June 22, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Grey to dark grey with waxy luster; Crystal structure: Trigonal (microscopic); Fracture: Conchoidal; Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or chemical precipitation from groundwater. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and starting fires; currently used in decorative landscaping, as an abrasive, and occasionally in jewelry as cabochons.

Geological facts

Chert is so hard it can scratch steel. When broken, it creates extremely sharp edges, which is why it was the primary material for prehistoric arrowheads and knives.

Field identification & locations

Identify by its waxy appearance, extreme hardness, and smooth, curved (conchoidal) fracture surfaces. Commonly found in riverbeds or eroded from limestone outcroppings.