sedimentary

Chert (and Jasper)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, white, and rusty orange; Luster: Dull to waxy; Structure: Cryptocrystalline; Fracture: Conchoidal (smooth, curved breaks); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, brown, white, and rusty orange
Luster: Dull to waxy

Identified June 30, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, brown, white, and rusty orange; Luster: Dull to waxy; Structure: Cryptocrystalline; Fracture: Conchoidal (smooth, curved breaks); Specific Gravity: 2.65

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or via chemical precipitation from silica-rich fluids within sedimentary rock layers, often limestone or dolomite.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used as road aggregate, landscaping stone, and occasionally in lapidary work for jewelry if colorful.

Geological facts

Chert is so durable that it often remains as 'float' long after the surrounding limestone bedrock has weathered away. It was one of the most important minerals for early human survival.

Field identification & locations

Identify by its high hardness (it will scratch glass or steel), smooth waxy feel on fresh surfaces, and circular 'conchoidal' fracture patterns. Common in riverbeds and limestone outcrops.