sedimentary
Chert / Jasper
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs); Color: Brown, tan, and dark grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.6
- Hardness
- 6
- Color
- Brown, tan, and dark grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Brown, tan, and dark grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.6
Formation & geological history
Formed by the accumulation of siliceous remains of organisms or chemical precipitation from fluids in sedimentary environments. Common in marine or lake bed deposits of various geological ages.
Uses & applications
Used historically for stone tools and arrowheads; currently used as landscaping stone, abrasive, or for lapidary work (jewelry and cabochons).
Geological facts
It has a conchoidal fracture which allows it to break into very sharp edges, a property that was vital to prehistoric civilizations for creating survival tools.
Field identification & locations
Identify by its waxy texture, extreme hardness (scratches glass), and the way it breaks along curved, shell-like surfaces. Found globally in river beds, deserts, and limestone formations.
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