sedimentary
Jasper or Chalcedony
Microcrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale. Color: Tan, brown, and translucent white. Luster: Waxy to vitreous. Crystal structure: Trigonal/Microcrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6–2.65.
- Hardness
- 6
- Color
- Tan, brown, and translucent white
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5–7 on Mohs scale. Color: Tan, brown, and translucent white. Luster: Waxy to vitreous. Crystal structure: Trigonal/Microcrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6–2.65.
Formation & geological history
Formed from the precipitation of silica from groundwater in the cavities of volcanic rocks or sedimentary layers. It can form over millions of years at low temperatures.
Uses & applications
Commonly used for lapidary work, decorative stone carvings, tumbling for rock collections, and historically for stone tools.
Geological facts
Chalcedony was used in the ancient world for seals and jewelry. Jasper is a variety containing impurities that render it opaque and often colorful.
Field identification & locations
Look for a smooth, waxy surface and a conchoidal (shell-like) fracture pattern. Found globally in riverbeds, deserts, and volcanic regions. It is much harder than glass and will scratch a steel knife blade.
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