sedimentary
Chert (Jasper and Chalcedony)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: tan, white, and reddish-brown, Luster: waxy to dull, Crystal structure: microcrystalline/cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.58–2.91
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: tan, white, and reddish-brown, Luster: waxy to dull, Crystal structure: microcrystalline/cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.58–2.91
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation from silica-rich fluids within sedimentary rock layers, often found in limestone or volcanic ash deposits.
Uses & applications
Historically used for stone tools and arrowheads; currently used for lapidary work, jewelry (cabs), and as decorative landscape stones.
Geological facts
This specimen shows the transition between common chert and red jasper. Jasper gets its red color from iron inclusions. Because of its conchoidal fracture, it was one of the most important materials for early human technology.
Field identification & locations
Identify in the field by its hardness (will scratch steel), waxy luster on fresh surfaces, and scalloped conchoidal fractures. Commonly found in river beds or erosion zones near limestone outcrops.
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