sedimentary
Chert (Jasper)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs), Color: reddish-brown and grayish-tan bands, Luster: dull to waxy/greasy, Crystal structure: Microcrystalline (trigonal), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs), Color: reddish-brown and grayish-tan bands, Luster: dull to waxy/greasy, Crystal structure: Microcrystalline (trigonal), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolarians) or chemical precipitation from silica-rich fluids within sedimentary rock layers. Its banded appearance suggests varying mineral content during deposition.
Uses & applications
Used historically for stone tools and weapons due to its sharp edges; currently used for lapidary work, jewelry (cabochons), and as a decorative landscaping stone.
Geological facts
This specimen shows distinct banding, often referred to as 'ribbon chert' or 'striped jasper.' Jasper is essentially an opaque variety of chert colored by iron impurities.
Field identification & locations
Identify in the field by its hardness (it can scratch glass and steel), conchoidal fracture (smooth, curved breaks), and lack of reaction to acid. Often found in riverbeds or coastal cliffs.
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