sedimentary
Chert (Mudstone)
Microcrystalline Quartz (SiO2)
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
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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.
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Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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