sedimentary
Chert (Common Opal/Jasper mix)
Silicon Dioxide (SiO2) with impurities
Hardness: 6.5-7. Color: Multi-colored (green, tan, brown). Luster: Waxy to resinous. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Multi-colored (green, tan, brown)
- Luster
- Waxy to resinous
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Physical properties
Hardness: 6.5-7. Color: Multi-colored (green, tan, brown). Luster: Waxy to resinous. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the accumulation of silica-rich fluids in sedimentary basins or volcanic ash beds, often replacing organic or volcanic material over millions of years.
Uses & applications
Lapidary work for cabochons, knapping for primitive tools/arrowheads, and used in landscaping or as collector rough.
Geological facts
The specimen exhibits a classic conchoidal (shell-like) fracture pattern common in silica rocks, which was historically utilized by early humans to make sharp tools.
Field identification & locations
Look for a glassy or waxy texture and sharp, curved edges where broken. Commonly found in river beds or areas with exposed sedimentary or old volcanic strata.
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