sedimentary
Chert (Yellow Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs), Color: Yellow, grey and brownish bands, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs), Color: Yellow, grey and brownish bands, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation from fluids in sedimentary environments. Common in marine limestone sequences or as river-worn nodules.
Uses & applications
Used historically for stone tools due to its sharp edges; used today as a lapidary material for polishing, in landscaping, and as a common collectible.
Geological facts
Chert is so durable that it often survives long-distance transport in rivers, which is why it is frequently found as rounded pebbles in sand and gravel deposits. Arrowheads and scrapers were often fashioned from this material by prehistoric humans.
Field identification & locations
Identify in the field by its waxy appearance and smooth, shell-like (conchoidal) fracture pattern. It will easily scratch glass and cannot be scratched by a steel pocketknife.
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