sedimentary
Jasper
Silicon dioxide (SiO2) with iron impurities
Hardness: 6.5–7 on Mohs scale; Color: Dark brown to reddish-brown (likely due to iron oxide); Luster: Waxy to dull; Crystal structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.58–2.91.
- Hardness
- 6
- Color
- Dark brown to reddish-brown (likely due to iron oxide)
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Dark brown to reddish-brown (likely due to iron oxide); Luster: Waxy to dull; Crystal structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.58–2.91.
Formation & geological history
Formed from the deposition of silica in hydrothermal veins or as a chemical precipitate in sedimentary environments. Its brown color results from high concentrations of iron oxide or hydroxide within the crystal structure. It often originates from ancient silica-rich seafloor deposits.
Uses & applications
Used in the lapidary arts for gemstones, cabochons, and ornamental carvings. Also used as a decorative stone in landscaping and historically for making tools due to its conchoidal fracture which creates sharp edges.
Geological facts
Jasper was a favorite gem in the ancient world, referenced in many historical and religious texts. It is an opaque variety of chalcedony that can contain up to 20% foreign materials, which accounts for its wide variety of colors and patterns.
Field identification & locations
Identify in the field by its hardness (will scratch glass but not quartz), waxy texture, and total opacity. Often found as rounded water-worn pebbles in riverbeds or beaches, particularly in areas with volcanic or sedimentary history.
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