sedimentary
Chert (Yellow Jasper variant)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Opaque yellow-brown with a waxy luster; Crystal Structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Opaque yellow-brown with a waxy luster
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Physical properties
Hardness: 6.5-7 Mohs; Color: Opaque yellow-brown with a waxy luster; Crystal Structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the accumulation of silica-rich micro-organisms or chemical precipitation in marine environments, followed by diagenetic replacement. Often found as nodules in limestone or as distinct bedded deposits.
Uses & applications
Used historically for stone tools due to sharp edges; currently used for ornamental stones, lapidary work, jewelry, and as aquarium gravel.
Geological facts
Chert has been used by humans for millions of years to make arrowheads and scrapers. The yellow color is typically caused by goethite or limonite inclusions.
Field identification & locations
Identify by its waxy luster, hardness (it will scratch glass), and conchoidal (shell-like) fracture. Found globally in sedimentary basins and along gravel-rich beaches.
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