sedimentary
Chert (specifically Jasper/Brown Chert)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brown, earthy ochre, or tan; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brown, earthy ochre, or tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brown, earthy ochre, or tan; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in sedimentary environments. Common in Paleozoic to Cenozoic rock layers.
Uses & applications
Historically used for stone tools/arrowheads due to its sharp edges; modernly used in jewelry (cabochons), landscaping, and as an abrasive in industrial applications.
Geological facts
Chert is so durable that it often survives as stream gravel long after the surrounding rock has eroded. High-quality brown jasper is often referred to as 'Egyptian Marble' or 'Mookite' depending on the specific region and patterns.
Field identification & locations
Identify by its 'flint-like' smooth, curved (conchoidal) breaks and its ability to scratch glass. Commonly found in riverbeds, glacial till, and embedded within limestone or dolomite formations.
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