sedimentary
Chert (Yellow Jasper variant)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Yellowish-brown to tan (stained by iron oxides); Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
- Hardness
- 7 on Mohs scale
- Color
- Yellowish-brown to tan (stained by iron oxides)
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellowish-brown to tan (stained by iron oxides); Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
Formation & geological history
Formed via the accumulation of silica-rich microfossils or chemical precipitation in sedimentary basins. Diagenetic processes replace original limestone or chalk with silica over millions of years.
Uses & applications
Historically used for stone tools (knapping) due to sharp edges; currently used for decorative gravel, landscaping, and lapidary tumbling.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most important minerals for early humans to create arrowheads and scrapers.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture patterns and ability to scratch glass. Found globally in limestone layers or as weathered nodules in stream beds.
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