sedimentary
Chert (var. Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs); Color: Reddish-brown; Luster: Dull to waxy; Crystal Structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Reddish-brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Reddish-brown; Luster: Dull to waxy; Crystal Structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the accumulation of silica-rich microfossils or chemical precipitation in sedimentary basins. The reddish hue is due to iron oxide inclusions.
Uses & applications
Historically used for stone tools (arrowheads). Today used in jewelry, lapidary arts, and as landscaping stone.
Geological facts
Chert and jasper have been used by humans for millions of years to create sharp-edged tools due to their conchoidal fracturing.
Field identification & locations
Identify by its hardness (it will scratch glass), its waxy feel, and the way it breaks into smooth, curved surfaces. Common in riverbeds and ancient seafloors.
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