sedimentary
Jasper and Quartz River Pebble
Silicon Dioxide (SiO2) with impurities
Hardness: 6.5-7 (Mohs scale); Color: bicolored with yellowish-translucent (quartz) and reddish-brown/purple (ferruginous jasper); Luster: waxy to sub-vitreous; Structure: cryptocrystalline/microcrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.9
- Hardness
- 6
- Luster
- waxy to sub-vitreous
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: bicolored with yellowish-translucent (quartz) and reddish-brown/purple (ferruginous jasper); Luster: waxy to sub-vitreous; Structure: cryptocrystalline/microcrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.9
Formation & geological history
Formed from silica-rich fluids precipitating in voids or replacing sedimentary structures, often enriched with iron oxides for the dark color. This specimen is water-worn, likely from an ancient riverbed or glacial deposit. Geological age can range from 10 million to over 1 billion years depending on the source deposit.
Uses & applications
Used primarily for lapidary work (tumbling, cabochons), landscape decoration, and as a low-cost collectible for rockhounds. Quartz and jasper are also used industrially for abrasives.
Geological facts
The distinct line between the two materials is a 'contact zone' where two different pulses of silica mineralization met. Jasper gets its red/purple hue from finely dispersed hematite or magnetite inclusions.
Field identification & locations
Identify by its hardness (will scratch glass), smooth water-worn texture, and bicolored appearance. These are commonly found in gravel pits, riverbanks, and beaches across the United States, particularly in the Great Lakes region and the Pacific Northwest.
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