sedimentary
Chert (Brecciated or Banded Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Brown, tan, and cream-white, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.6-2.7.
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Brown, tan, and cream-white, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.6-2.7.
Formation & geological history
Formed usually by the replacement of calcium carbonate by silica in marine or groundwater environments. This specific specimen has been weathered and water-worn into a smooth river pebble shape.
Uses & applications
Historically used for stone tools (arrowheads). Today used as decorative gravel, in road construction, and as tumbling material for hobbyists.
Geological facts
Chert is known for its ability to produce sparks when struck against steel. It is one of the most durable rocks on the planet, often surviving extreme weathering that dissolves other stones.
Field identification & locations
Identify in the field by its hardness (it should scratch glass) and its smooth, waxy texture. Commonly found in riverbeds, coastal beaches, and limestone outcrops globally.
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