sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Off-white, tan, and creamy beige with some translucency; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Off-white, tan, and creamy beige with some translucency
Luster: Waxy to vitreous

Identified May 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily through the chemical precipitation of silica-rich fluids within sedimentary basins, often replacing organic material or carbonate rocks. This specimen appears to be a weathered or worked fragment, common in paleo-environments.

Uses & applications

Historically used for making stone tools (knapping) such as arrowheads and scrapers. Modern uses include abrasives, road ballast, and as a component in glass manufacturing.

Geological facts

Chert is so durable that it often remains in the soil long after the surrounding limestone or chalk has weathered away. It was one of the first materials exploited by early humans for tool development due to its predictable fracture patterns.

Field identification & locations

Identified in the field by its hardness (scratches glass), waxy feel, and sharp conchoidal (shell-like) fractures. It is commonly found in limestone or chalk beds globally. This specific piece shows a possible 'bulb of percussion' or flake scar, suggesting it may be a debitage flake from lithic reduction.