sedimentary
Chert (Jasper variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Brown, tan, and reddish-white; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brown, tan, and reddish-white
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, tan, and reddish-white; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the microcrystalline accumulation of silica, often in marine environments where silica-rich fluids replace organic material or precipitate in voids within limestone or shale.
Uses & applications
Historically used for stone tools (arrowheads); currently used in jewelry (as Jasper), aquarium decor, and as an industrial abrasive.
Geological facts
Chert was one of the first materials used by early humans for tools because it breaks with a very sharp, glass-like conchoidal fracture. This specific piece shows the typical angular, splintery habit of broken chert.
Field identification & locations
Identify in the field by its hardness (will scratch glass), waxy luster on fresh surfaces, and smooth, curved fracture lines. It is common in limestone regions and riverbeds.
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