sedimentary
Chert (Jasper)
Microcrystalline Quartz (SiO2) with iron oxide impurities
Hardness: 6.5-7 Mohs; Color: Brownish-red to dark tan; Luster: Waxy to sub-glassy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Brownish-red to dark tan
- Luster
- Waxy to sub-glassy
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brownish-red to dark tan; Luster: Waxy to sub-glassy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed primarily through the chemical precipitation of silica or the accumulation of silica-rich organic remains (like radiolarians) in marine environments. This specimen appears water-worn, likely from a stream or river bed.
Uses & applications
Historically used for stone tools due to its sharp edges; modernly used for decorative stones, lapidary work (jewelry), and occasionally as an industrial abrasive.
Geological facts
Chert has been used by humans for hundreds of thousands of years to create arrowheads and scrapers. Darker, opaque varieties containing iron oxides are specifically termed Jasper.
Field identification & locations
Identify in the field by its hardness (will scratch glass), waxy feel, and smooth, curved (conchoidal) fracture surfaces. Commonly found in river gravels or sedimentary rock outcrops.
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