sedimentary
Chert Pebble (with Quartz Vein)
Chert (Cryptocrystalline Silica - SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, and white; Luster: Waxy to dull; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, and white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, and white; Luster: Waxy to dull; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. This specimen is a water-worn river or beach pebble, likely showing a secondary quartz vein and oxidation staining.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to sharp edges; currently used for road gravel, decorative landscaping, and occasionally lapidary tumbling.
Geological facts
Chert is so durable that it resists weathering better than surrounding rocks, often remaining as rounded pebbles in stream beds long after the parent rock has eroded away. Historically, flint (a variety of chert) was essential for starting fires.
Field identification & locations
Identify by its 'waxy' texture, extreme hardness (it will scratch glass and steel), and smooth, rounded shape from water erosion. Found globally in gravel pits, riverbeds, and ocean beaches.
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