sedimentary
Chert (Jasper/River Pebble)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, and reddish hues; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brown, tan, and reddish hues
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, and reddish hues; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils or precipitation from silica-rich fluids in sedimentary environments. Its rounded shape indicates it has been tumbled and eroded in a river or stream over thousands of years.
Uses & applications
Historically used for stone tools and arrowheads; currently used as landscaping gravel, in jewelry as 'river stone' beads, or for rock tumbling and collecting.
Geological facts
Chert is extremely durable and chemically stable, which is why it often survives as rounded pebbles long after other rocks have eroded away. Varieties containing iron oxides are often called Jasper.
Field identification & locations
Identify in the field by its smooth texture, waxy luster when wet, and its ability to scratch glass. It is commonly found in riverbeds, glacial tills, and beaches.
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