sedimentary
Chert (Jasper/Common Chert Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Brownish-tan to earthy orange, Luster: Waxy to dull, Crystal Structure: Trigonal/Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Brownish-tan to earthy orange, Luster: Waxy to dull, Crystal Structure: Trigonal/Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. This pebble appears to be mechanically weathered and water-worn from a larger sedimentary deposit.
Uses & applications
Common varieties are used for road aggregate and construction. Higher quality Jasper is used in lapidary work and jewelry. Historically used for stone tools and fire-starting (flint).
Geological facts
Chert is so hard it can scratch steel. It breaks with sharp 'conchoidal' edges, which made it the primary material for prehistoric arrowheads and tools for millions of years.
Field identification & locations
Identify in the field by its waxy luster, extreme hardness, and smooth, rounded water-worn surface. Commonly found in riverbeds, gravel pits, and glacial till worldwide.
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