sedimentary
Chert (specifically brown Chert or Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Dark brown to reddish-brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 Mohs scale
- Color
- Dark brown to reddish-brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Dark brown to reddish-brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in sedimentary environments. Common in marine limestone formations.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges when fractured. Currently used in lapidary work, jewelry (especially when colorful like Jasper), and as architectural aggregate.
Geological facts
Chert is one of the most durable sedimentary rocks. It was historically valuable for striking fire against steel, similar to flint. It is also a very common rock found in riverbeds and glacial deposits.
Field identification & locations
Identified in the field by its conchoidal (shell-like) fracture, waxy luster, and its ability to scratch glass. Found globally in creek beds, beaches, and sedimentary outcrops.
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