sedimentary
Chert (potentially Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Dark brown to tan banding; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 Mohs scale
- Color
- Dark brown to tan banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Dark brown to tan banding; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed primarily through the accumulation of silica-rich organic remains or chemical precipitation within sedimentary layers. This process creates dense, microcrystalline structures often showing banding from varying mineral impurities.
Uses & applications
Historically used for stone tools and arrowheads; currently used in decorative landscaping, as a construction aggregate, and occasionally in lapidary work if highly colorful.
Geological facts
Because it breaks with a conchoidal fracture like glass, chert was one of the most important materials for prehistoric humans to create sharp cutting tools. Most chert is hundreds of millions of years old.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel knife) and its smooth, glass-like fracture surfaces. Often found in riverbeds or as nodules within limestone or chalk formations.
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