sedimentary
Chert (Jasper/Limonitic Chert)
Cryptocrystalline Quartz (SiO2) with Iron Oxide (FeO(OH)) inclusions
Hardness: 6.5-7 (Mohs), Color: Ochre-brown to earthy yellow, Luster: Dull to waxy, Crystal Structure: Hexagonal (cryptocrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs), Color: Ochre-brown to earthy yellow, Luster: Dull to waxy, Crystal Structure: Hexagonal (cryptocrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Biogenic or chemical precipitation of silica in marine or groundwater environments. This specimen is rich in limonite/goethite, giving it a rusty brown color. It can range in age from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and flintknapping. Currently used as an ornamental stone, lapidary material, and sometimes as road aggregate or industrial filler.
Geological facts
This variety of chert is often called 'Yellow Jasper' in the gem trade. Because it is harder than steel, it will create sparks when struck against iron, making it a reliable fire-starter throughout human history.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. It feels very dense and smooth to the touch compared to sandstone.
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