sedimentary
Chert (Jasper variation)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Brownish-red, ochre, and dark grey; Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brownish-red, ochre, and dark grey
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Brownish-red, ochre, and dark grey; Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation from silica-rich fluids within sedimentary environments. This specimen appears weathered and may have been transported by water or glaciers.
Uses & applications
Historically used for making stone tools (arrowheads/knives) due to its sharp edges when broken. Today used as an abrasive, in landscaping, and as a semi-precious gemstone when polished.
Geological facts
Chert is so durable it often survives long after the surrounding rock has eroded away. It is essentially a non-banded form of chalcedony.
Field identification & locations
Identify by its 'conchoidal' (shell-like) fracture pattern and its ability to scratch glass. Commonly found in stream beds, gravel pits, and limestone outcrops.
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