sedimentary

Chert (Flinty variety)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

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

Hardness: 7 on Mohs scale
Color: Tan, brown, and grey with iron oxide staining
Luster: Dull to waxy

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, brown, and grey with iron oxide staining; 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 within limestone or chalk beds.

Uses & applications

Historically used for stone tools and fire-starting. Currently used in road surfacing, as an abrasive, and sometimes in landscaping or decorative masonry.

Geological facts

Because of its conchoidal fracture (breaking like glass), chert was one of the primary materials used by prehistoric humans to create sharp arrowheads, scrapers, and knives.

Field identification & locations

Identify by its hardness (it will scratch glass) and its sharp, curved fracture edges. Commonly found in riverbeds or eroding out of limestone outcrops. Look for its characteristic waxy texture on freshly broken surfaces.