sedimentary
Chert (Yellow Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: yellowish-brown, translucent to opaque; Luster: waxy to dull; Fracture: conchoidal; Crystal system: Trigonal (microcrystalline)
- Hardness
- 6
- Color
- yellowish-brown, translucent to opaque
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: yellowish-brown, translucent to opaque; Luster: waxy to dull; Fracture: conchoidal; Crystal system: Trigonal (microcrystalline)
Formation & geological history
Formed from the accumulation of silica-rich fluids in sedimentary environments or the replacement of limestone. Can take millions of years to stabilize from opal-CT to quartz.
Uses & applications
Commonly used for lapidary work (tumbling/polishing), historical tool making (arrowheads), and as decorative gravel.
Geological facts
Chert and jasper are among the oldest materials used by early humans for stone tools because of their ability to break with sharp edges.
Field identification & locations
Look for a waxy luster and smooth, shell-like (conchoidal) fractures. Often found in riverbeds or as nodules within limestone formations.
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