sedimentary

Chert (Brown Variety)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5–7 on Mohs scale; Color: Dull brown to tan; Luster: Waxy to sub-glassy; Crystal structure: Cryptocrystalline (hexagonal system at microscopic level); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 6
Color: Dull brown to tan
Luster: Waxy to sub-glassy

Identified June 12, 2026More sedimentary →

Explore Chert (Brown Variety) in the encyclopedia →

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Physical properties

Formation & geological history

Formed by the accumulation of siliceous remains of marine organisms or by chemical precipitation from silica-rich groundwater within limestone or chalk beds. It can date from the Precambrian to Cenozoic eras.

Uses & applications

Historically used for stone tools (lithics) due to its sharp edges when broken. High-quality varieties are used in jewelry and lapidary work. Crushed chert is used as a sub-base for roads and in concrete.

Geological facts

Chert is so hard that it can strike sparks against steel, which made it essential for flintlock firearms and early fire-starting kits. Brown chert is often referred to as 'jasper' if it is opaque and highly aesthetic.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture pattern and its inability to be scratched by a steel knife. It is common in riverbeds and limestone outcrops worldwide.