sedimentary
Chert (Jasper/Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Dull olive-green to tan, Luster: Waxy to vitreous, 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: Dull olive-green to tan, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the precipitation of silica-rich fluids in sedimentary environments or through the replacement of limestone. This specimen shows significant rounding due to water erosion, likely being a river or beach pebble.
Uses & applications
Historically used for stone tools due to its sharp conchoidal fracture. Modern uses include decorative gravel, landscaping, and lapidary work for tumbled stones.
Geological facts
Chert is so hard that it can scratch steel and produce sparks when struck against iron, a property utilized in ancient flintlock firearms and fire-starting kits.
Field identification & locations
Identify in the field by its hardness (it cannot be scratched by a knife), its smooth, waxy surface when wet, and the way it breaks into curved, shell-like (conchoidal) segments. Commonly found in riverbeds and gravel deposits.
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