sedimentary

Chert (Flint Nodules)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: typically grey, tan, or brown; Luster: dull to waxy; Texture: fine-grained/cryptocrystalline; Fractures: conchoidal (producing sharp edges).

Hardness: 7 on Mohs scale
Color: typically grey, tan, or brown
Luster: dull to waxy

Identified June 17, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: typically grey, tan, or brown; Luster: dull to waxy; Texture: fine-grained/cryptocrystalline; Fractures: conchoidal (producing sharp edges).

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation within limestone or chalk beds. Often found as nodules or concretions in marine sedimentary environments.

Uses & applications

Historically used for stone tools and starting fires; currently used in construction aggregates, road surfacing, and as a decorative stone in landscaping.

Geological facts

Because it breaks with a conchoidal fracture like glass, it was the primary material for prehistoric arrowheads and scrapers. It is chemically very resistant to weathering.

Field identification & locations

Identify by its hardness (will scratch glass), conchoidal fracture patterns, and smooth but dull appearance. Commonly found along riverbeds, beaches, and eroded limestone outcroppings.