sedimentary

Chert (Brown Flint)

Cryptocrystalline or Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs; Color: Brown, tan, ochre; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs
Color: Brown, tan, ochre
Luster: Waxy to dull

Identified July 2, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Brown, tan, ochre; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed primarily through the chemical precipitation of silica from seawater or ground fluids. It often accumulates as nodules in limestone or chalk beds. This specimen appears stream-rounded, suggesting extensive transport by water.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Today used as road aggregate, in landscaping, and occasionally as a low-cost lapidary material.

Geological facts

Chert is so durable that it is often the only material left when the surrounding limestone weathers away. Some chert contains microscopic fossils called radiolarians or diatoms.

Field identification & locations

Identified by its waxy appearance, smooth feel, and ability to scratch glass. It will produce a spark when struck against steel. Commonly found in riverbeds, gravel pits, and coastal areas.