sedimentary
Chert (Yellow Jasper/River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs), Color: Yellowish-tan to grey, Luster: Waxy to vitreous when wet, Structure: Cryptocrystalline, Fracture: Conchoidal
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs), Color: Yellowish-tan to grey, Luster: Waxy to vitreous when wet, Structure: Cryptocrystalline, Fracture: Conchoidal
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of siliceous organisms in marine environments. This specimen shows significant rounding from fluvial (river) erosion.
Uses & applications
Commonly used in landscaping, as a gemstone for tumbling, and historically used for stone tools due to its conchoidal fracture.
Geological facts
Chert and jasper have been used by humans for hundreds of thousands of years to create arrowheads and scrapers because they break with extremely sharp edges.
Field identification & locations
Identify by its hardness (it will scratch glass), its smooth waxy feel, and the way it rounds into smooth 'potatoes' in riverbeds. Found globally in alluvial deposits.
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