sedimentary

Chert (Mudstone)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, olive-drab; Luster: Dull to waxy; Structure: Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.6

Hardness: 6
Color: Brown, tan, olive-drab
Luster: Dull to waxy

Identified April 2, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, olive-drab; Luster: Dull to waxy; Structure: Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.6

Formation & geological history

Formed from the accumulation of silica-rich organic remains or chemical precipitation within marine or lacustrine sediment layers, often during the Paleozoic or Mesozoic eras.

Uses & applications

Historically used for stone tools and fire-starting; currently used as construction aggregate, road base, and occasionally as a low-cost tumbled gemstone.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges, ideal for arrowheads and scrapers.

Field identification & locations

Identify by its hardness (it will scratch glass) and its smooth, waxy feel compared to rougher sandstone. Often found as nodules in limestone or as smooth river pebbles.