sedimentary
Chert (Jasper/Carnelian variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Reddish-brown, tan, or orange; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Reddish-brown, tan, or orange
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Reddish-brown, tan, or orange; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils on the seafloor or by the replacement of carbonate minerals by silica-rich fluids. This specimen shows significant rounding from river or water transport.
Uses & applications
Historically used for stone tools; currently used as decorative gravel, in lapidary work (tumbling/cabochons), and as low-cost gemstones in jewelry.
Geological facts
Chert is so hard and dense that it was commonly used by prehistoric humans to create sharp scraping and cutting tools. The reddish tint is usually caused by trace amounts of iron oxide.
Field identification & locations
Identify by its 'waxy' texture when wet or polished, its inability to be scratched by a steel knife, and its smooth, rounded shape. Commonly found in riverbeds, gravel pits, and glacial till throughout North America.
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