sedimentary
Jasper Chert
Microcrystalline Quartz (SiO2) with iron oxide inclusions
Hardness: 6.5-7 on Mohs scale. Color: Reddish-brown to tan. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.9.
- Hardness
- 6
- Color
- Reddish-brown to tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Reddish-brown to tan. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.9.
Formation & geological history
Formed from the accumulation of silica-rich micro-organisms or chemical precipitation in marine environments, subsequently enriched with iron oxides. These often occur as nodules within limestone or as river-tumbled pebbles.
Uses & applications
Commonly used for lapidary work (cabs), tumbled stones, and historically for primitive tools like scrapers and arrowheads due to its sharp fracture edge.
Geological facts
Red jasper specifically gets its color from high concentrations of iron. It has been used since antiquity for seals and amulets, and is mentioned frequently in historical and religious texts as a significant stone.
Field identification & locations
Field identification is based on its hardness (it will scratch glass), its smooth, waxy surface when wet, and its characteristic curved (conchoidal) fracture pattern. Found globally in riverbeds and ancient coastal sediments.
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