sedimentary
Chert (Jasper variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Brownish-red to tan. Luster: Dull to waxy. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Brownish-red to tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Brownish-red to tan. Luster: Dull to waxy. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed via the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Common in marine deposits where silica replaces limestone or marrow.
Uses & applications
Historically used for stone tools (flintknapping); currently used in landscaping, tumbling for lapidary use, and as a component in construction aggregate.
Geological facts
Chert has been used by humans for millions of years to create sharp-edged tools like arrowheads and scrapers. Jasper is the name specifically given to opaque, impure varieties of chert often colored by iron oxides.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Common in riverbeds and gravel pits.
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