sedimentary
Chert (Jasper/Agate variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs), Color: Pinkish-tan with possible banding, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline (Microscopic quartz), Fracture: Conchoidal
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs), Color: Pinkish-tan with possible banding, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline (Microscopic quartz), Fracture: Conchoidal
Formation & geological history
Formed from the chemical precipitation of silica or the accumulation of siliceous remains of microorganisms (radiolarians or diatoms) in marine environments.
Uses & applications
Primarily used for landscape gravel, historical stone tool making (knapping), and as a decorative specimen if colorful.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has weathered away. It was one of the most important materials for early humans to create arrowheads and scrapers.
Field identification & locations
Identify by its hardness (scratches glass) and smooth, shell-like (conchoidal) fractures. Common in limestone deposits and riverbeds.
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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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Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
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Sandstone
Arenite (primarily SiO2)
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