sedimentary
Chert (or Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Brown, tan, reddish; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Brown, tan, reddish
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Brown, tan, reddish; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed by the precipitation of silica in marine environments or through the replacement of limestone by silica-rich fluids. Can be found in many geological formations globally.
Uses & applications
Historically used for making stone tools (arrowheads). Today used as aquarium gravel, landscaping stone, and occasionally for lapidary work if it has attractive banding.
Geological facts
Because it is harder than steel and breaks with sharp edges, it was one of the most important minerals for early humans to create survival tools.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and smooth, curved conchoidal fractures. Commonly found in stream beds or as nodules in limestone.
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