sedimentary

Chert (Jasper/Limonitic Chert)

Cryptocrystalline Quartz (SiO2) with Iron Oxide (FeO(OH)) inclusions

AI-generated identification · may be incorrect

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

Identified July 14, 2026More sedimentary →

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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.