sedimentary
Chert (often called Jasper in this color)
Microcrystalline quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Reddish-brown/Tan, 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: Reddish-brown/Tan, 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 organic remains or chemical precipitation in oceanic or lacustrine environments. Most specimens range from hundreds of millions to billions of years old.
Uses & applications
Historical use for stone tools/arrowheads due to sharp fracture edges; modern use in lapidary work, landscaping, and as a decorative gemstone.
Geological facts
Chert is so durable that it often survives as rounded pebbles in riverbeds and on beaches long after the surrounding softer rock has eroded away. Historically, flint (a variety of chert) was essential for starting fires.
Field identification & locations
Identify in the field by its waxy texture, inability to be scratched by a steel knife, and characteristic 'clamshell' (conchoidal) fractures. Often found in river gravels or as nodules in limestone.
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