sedimentary

Chert (variations include Flint or Jasper)

Silicon Dioxide (SiO2)

Hardness: 7.0 Mohs; Color: Brown, grey, and tan (as seen in specimen); Luster: Waxy to dull; Structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal/shell-like fracture); Specific gravity: 2.5-2.8

Hardness: 7
Color: Brown, grey, and tan (as seen in specimen)
Luster: Waxy to dull

Identified March 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. This specimen shows a weathered exterior 'rind' with a darker, unweathered interior.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to sharp edges; currently used for road surfacing, decorative landscaping, and occasionally as semi-precious gemstones (jasper).

Geological facts

Because it fractures into razor-sharp edges, chert was the primary material for the Stone Age technology for millions of years. It is chemically very stable and can survive for billions of years in the rock record.

Field identification & locations

Identify by its 'conchoidal' fracture (smooth, curved breaks like broken glass) and high hardness—it will easily scratch glass or steel. Common in limestone riverbeds and gravel pits.

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