sedimentary
Chert (Jasper/Agate variety)
Microcrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, cream, and brown; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, cream, and brown
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, cream, and brown; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation from silica-saturated fluids in sedimentary environments. Common in marine limestone/chalk or river gravels.
Uses & applications
Historically used for edge tools (flintknapping) due to its sharp fracture. Currently used as decorative landscaping stone, in road base, and for amateur lapidary (tumbling/polishing).
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most important materials for prehistoric humans to create arrowheads and scrapers.
Field identification & locations
Identify in the field by its waxy texture and shell-like (conchoidal) fractures. Often found as rounded river pebbles or nodules within limestone outcrops. Common worldwide in fluvial deposits.
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