sedimentary
Chert (Jasper variety)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 6.5–7 on Mohs scale; Color: Reddish-brown, orange-red; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- Reddish-brown, orange-red
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Reddish-brown, orange-red; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the precipitation of silica from seawater or groundwater. This specific reddish color indicates the presence of iron oxide (hematite) impurities. It can form in deep-sea deposits or as replacement nodules in limestone.
Uses & applications
Historically used for making stone tools (flint knapping) due to its sharp edges when broken. Today used in jewelry as semi-precious gemstones (cabs), tumbling for lapidary hobbies, and as decorative landscaping stone.
Geological facts
Jasper has been used by humans for millions of years. It was a favorite for seal-stones in Minoan Crete. Because it is so hard and chemically stable, it often survives as rounded pebbles in riverbeds and on beaches long after the surrounding rock has eroded.
Field identification & locations
Identify in the field by its smooth, waxy texture and conchoidal (shell-like) fracture pattern. It will easily scratch glass but cannot be scratched by a steel knife. Commonly found in river gravels, desert pavements, and coastal beaches.
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