sedimentary
Jasper
Jasper (Silica-rich Microcrystalline Quartz, SiO2)
Hardness: 6.5–7 (Mohs scale); Color: Brown, tan, reddish tones; Luster: Dull to waxy; Structure: Microcrystalline (Cryptocrystalline); Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.58–2.91.
- Hardness
- 6
- Color
- Brown, tan, reddish tones
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5–7 (Mohs scale); Color: Brown, tan, reddish tones; Luster: Dull to waxy; Structure: Microcrystalline (Cryptocrystalline); Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.58–2.91.
Formation & geological history
Usually forms in sedimentary environments when silica-rich fluids permeate through volcanic ash or sediment. Over long geological periods, the silica crystallizes into a dense, opaque mineral. This specimen appears stream-worn or weather-rounded.
Uses & applications
Commonly used in lapidary work for making cabochons, beads, and ornaments. In industry, it was historically used as a touchstone for testing precious metals.
Geological facts
The brown color typically comes from iron oxide (limonite or goethite) inclusions. Jasper has been used since ancient times for cylinders, seals, and amulets, often mentioned in biblical and ancient Greek literature.
Field identification & locations
Identify in the field by its opacity (even thin edges won't transmit light), hardness (cannot be scratched by a steel knife), and smooth, rounded water-worn texture. Frequently found in riverbeds and coastal areas.
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