sedimentary
Chert (Jasper variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, earthy red; Luster: Dull to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brown, tan, earthy red
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, earthy red; Luster: Dull to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from silica-rich fluids in sedimentary environments. Common in marine or riverbed deposits.
Uses & applications
Historically used for stone tools (flintknapping); currently used for decorative landscaping, lapidary arts (polishing), and as drainage gravel.
Geological facts
Chert and its variety Jasper were essential to prehistoric humans because they break with extremely sharp, glass-like edges, making them ideal for arrowheads and knives.
Field identification & locations
Identify by its hardness (will scratch glass), smooth waxy feel when wet, and lack of visible grains. Common in riverbeds and as pebbles in glacial till.
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