sedimentary
Chert (Brown Flint)
Cryptocrystalline or Microcrystalline Quartz (SiO2)
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
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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.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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