sedimentary
Chert / Jasper
Sedimentary Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Red, yellow, and grey banding, Luster: Waxy to dull, Crystal Structure: 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: Red, yellow, and grey banding, Luster: Waxy to dull, Crystal Structure: Microcrystalline, 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-saturated fluids in marine or groundwater environments. This specimen shows oxidation (limonite/hematite staining) which gives the red and yellow coloring.
Uses & applications
Historically used for stone tools (arrowheads). Modernly used in landscaping, river rock decor, and as lapidary material for polishing into cabochons.
Geological facts
This specimen is often referred to as 'fancy chert' due to its multiple colors. It is incredibly durable and resistant to chemical weathering, which is why it remains as a smooth pebble in riverbeds long after other rocks have eroded.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds, glacial tills, and limestone deposits.
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