sedimentary
Chert (Jasper variety)
Silicon dioxide (SiO2) - Microcrystalline Quartz
Hardness: 6.5-7 (Mohs scale), Color: Yellow-brown to tan with darker inclusions, Luster: Waxy to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Yellow-brown to tan with darker inclusions, Luster: Waxy to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich fluids within sedimentary host rocks or from the silica shells of marine organisms. This specimen likely formed through diagenetic replacement of limestone or chalk.
Uses & applications
Used historically for stone tools and arrowheads due to its sharp conchoidal fracture. Today it is used in lapidary work, jewelry, and as decorative stone.
Geological facts
Chert is so durable that it survives weathering much longer than surrounding rocks. Yellow-brown varieties like this are often referred to as 'yellow jasper' in the gemstone trade.
Field identification & locations
Identify in the field by its sharp, glass-like edges when broken and its ability to scratch glass. It is commonly found in stream beds or as nodules protruding from weathered limestone cliffs.
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