sedimentary

Chert (concretionary/nodular variant)

Microcrystalline Quartz (SiO2) with possible fossil or mineral inclusions

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs); Color: Brown, tan, and white; Luster: Waxy to dull; Structure: Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.6-2.7

Hardness: 6
Color: Brown, tan, and white
Luster: Waxy to dull

Identified February 21, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Brown, tan, and white; Luster: Waxy to dull; Structure: Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.6-2.7

Formation & geological history

Formed via the precipitation of silica in sedimentary rock layers, often replacing organic matter or filling voids. This process typically occurs in marine environments over millions of years.

Uses & applications

Used historically for stone tools (arrowheads). Modern uses include road surfacing, decorative gemstones (jaspers), and as a raw material in some ceramic manufacturing.

Geological facts

Chert is extremely durable and chemical-resistant. Flint is a well-known dark variety of chert. The white 'potted' area in this specimen may be a localized concentration of calcite or silicious fossils.

Field identification & locations

Identified by its extreme hardness (scratches glass) and smooth, curved conchoidal fractures. Commonly found in limestone or chalk beds, riverbeds, and coastal areas.