sedimentary
Chert (Jasper/Agate variety)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs), Color: Translucent grey to opaque reddish-brown, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal
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Physical properties
Hardness: 7 (Mohs), Color: Translucent grey to opaque reddish-brown, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal
Formation & geological history
Formed as chemical precipitates from silica-rich fluids in sedimentary environments or as nodules in limestone. Often weathered and rounded by water transport.
Uses & applications
Used primarily in lapidary work for polishing, historical tool making (flint knapping), and as decorative gravel.
Geological facts
This specimen shows the smooth, water-worn texture typical of river rocks and exhibits conchoidal fracturing on its edges, a trait that allowed ancient humans to chip it into sharp points.
Field identification & locations
Identify in the field by its waxy luster, extreme hardness (it will scratch glass), and smooth, curved fracture surfaces. Commonly found in riverbeds and glacial deposits.
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