sedimentary
Chert (Yellow Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Yellow, tan, and brownish-grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
- Hardness
- 6
- Color
- Yellow, tan, and brownish-grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Yellow, tan, and brownish-grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
Formation & geological history
Formed from the accumulation of silica-rich microfossils or inorganic precipitation in sedimentary environments. Its yellow color often comes from iron inclusions (limonite or goethite).
Uses & applications
Primarily used for lapidary work, jewelry, and flint-knapping. Historically used by early humans for tools and arrowheads due to its sharp edges when broken.
Geological facts
Chert and Jasper are essentially the same mineral composition, but Jasper is typically the term used for colorful, opaque varieties. It is often found as nodules in limestone or as distinct bedded deposits.
Field identification & locations
Identify in the field by its conchoidal (shell-like) fracture patterns, sharp edges, and inability to be scratched by a steel knife. It is common in riverbeds and limestone outcrops worldwide.
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