sedimentary
Chert with Jasper and Quartz
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: Reddish-brown, white, and translucent blue-grey; Luster: Vitreous to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
- Hardness
- 7 Mohs
- Color
- Reddish-brown, white, and translucent blue-grey
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 Mohs; Color: Reddish-brown, white, and translucent blue-grey; Luster: Vitreous to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
Formation & geological history
Formed from the accumulation of silica-rich fluids in limestone or volcanic ash beds. This specimen displays a mix of jasper (red from iron inclusions) and common opal or translucent chalcedony.
Uses & applications
Historically used for stone tools and arrowheads. Currently used for lapidary work, cabochons, and as a collector's specimen.
Geological facts
This specimen shows 'brecciation' or mixing where different pulses of silica saturated water filled cavities, creating the distinct color zones. Chert is one of the most durable sedimentary rocks.
Field identification & locations
Identify by its hardness (will scratch glass) and smooth, shell-like (conchoidal) fracture surfaces. Commonly found in river beds or eroaded sedimentary basins.
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