sedimentary
Chert (Yellow Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Brownish-yellow to mustard; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 6
- Color
- Brownish-yellow to mustard
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brownish-yellow to mustard; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed as a sedimentary rock through the accumulation of silica-rich microfossils or precipitation from silica-rich fluids in limestone or chalk beds. Often contains iron oxides that provide the yellow/brown coloration.
Uses & applications
Used historically for stone tools and arrowheads due to its sharp edges; used today as a gemstone for jewelry, cabochons, and as a landscaping stone.
Geological facts
Chert has been used by humans for hundreds of thousands of years to create tools. Yellow chert/jasper is specifically prized in lapidary work for its ability to take a high polish.
Field identification & locations
Identified by its extremely smooth, waxy feel and conchoidal (shell-like) fracture edges. Commonly found in nodules inside sedimentary rock formations such as limestone.
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