sedimentary

Chert

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: Brown, tan, cream, and white mottling, Luster: Dull to waxy, Crystal Structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture)

Identified June 15, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: Brown, tan, cream, and white mottling, Luster: Dull to waxy, Crystal Structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture)

Formation & geological history

Formed by the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolaria) or by chemical precipitation from silica-rich groundwater replacing other minerals in carbonate rocks.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp fracture edges. Modernly used as road base, decorative landscaping stone, and occasionally in jewelry as jasper.

Geological facts

Chert is so hard it can strike sparks against steel, a property that was used for centuries in flintlock firearms and for starting fires. Variations are often called Flint (if dark/black) or Jasper (if red/yellow).

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its curved, shell-like (conchoidal) fracture surfaces. Commonly found in limestone and dolomite beds as nodules or layers.