sedimentary
Jasper (specifically Green Jasper/Chert)
Jasper (Silicon Dioxide, SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Dark green with lighter streaks or mottling; Luster: Vitreous to waxy; Crystal Structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.91
- Hardness
- 6
- Color
- Dark green with lighter streaks or mottling
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Dark green with lighter streaks or mottling; Luster: Vitreous to waxy; Crystal Structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.91
Formation & geological history
Formed from the chemical precipitation of silica-rich fluids in volcanic or sedimentary environments, often associated with hydrothermal activity or the accumulation of silica-based microorganisms (radiolarians). Dates vary by deposit, often appearing in Precambrian to Mesozoic layers.
Uses & applications
Primarily used in lapidary arts for jewelry, beads, cabochons, and ornamental carvings. Historically used for making tools and weapons (arrowheads) due to its conchoidal fracture.
Geological facts
Jasper has been used for millennia; in medieval times, green jasper was believed to have healing powers and the ability to bring rain. It is often opaque, which distinguishes it from its translucent cousin, chalcedony.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture. Commonly found in stream beds, gravel deposits, and mountainous regions like the Pacific Northwest or the Ural Mountains.
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