sedimentary
Chert (variously known as Flint or River Pebble)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale. Color: Tan, grey, and cream banding. Luster: Waxy to dull. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, grey, and cream banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: Tan, grey, and cream banding. Luster: Waxy to dull. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
Formation & geological history
Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or chemical precipitation in marine environments. This specimen shows significant rounding from water erosion (fluvial transport).
Uses & applications
Historically used for stone tools and strike-a-lights; currently used in construction aggregate, road base, and as decorative river stones in landscaping.
Geological facts
Chert is so hard it can scratch steel. When broken, it creates exceptionally sharp edges, which is why it was the primary material for prehistoric arrowheads and scrapers.
Field identification & locations
Identify by its 'waxy' texture and conchoidal (shell-like) fractures. It will not react to acid and is harder than a pocket knife blade. Common in riverbeds and limestone outcrops.
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