sedimentary
Chert (Jasper variety)
Silicon Dioxide (SiO2) - Cryptocrystalline Quartz
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6
- Hardness
- 6
- Color
- Brown, tan, reddish-brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from silica-rich fluids in sedimentary basins. Often found in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used today as decorative garden stones, in jewelry when colorful (Jasper), or for fire-starting with steel.
Geological facts
Because of its hardness and conchoidal fracture pattern, chert was one of the most important minerals for early humans to manufacture sharp-edged tools. It is exceptionally resistant to weathering.
Field identification & locations
Identify in the field by its smooth, waxy surface and shell-like (conchoidal) curved breaks. It will scratch glass easily. Commonly found in riverbeds or as nodules within limestone outcrops.
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