sedimentary

Chert (Tan/Brown variety)

Chert (Silicon Dioxide, SiO2)

Hardness: 7 on Mohs scale; Color: Tan, beige, or light brown; Luster: Dull to waxy; Crystal structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, beige, or light brown
Luster: Dull to waxy

Identified March 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or via chemical precipitation from silica-rich fluids in limestone or chalk beds. It can range from Precambrian to Cenozoic in age.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges; modernly used as road aggregate, in grinding media, and occasionally as decorative landscaping stone.

Geological facts

Chert is so hard it can strike sparks against steel, which made it essential for flintlock firearms; different colors of chert are often given unique names like Jasper (red) or Flint (dark grey/black).

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass easily. It is found globally, often appearing as nodules within limestone or as massive bedded deposits.

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Brecciated Chert (Microcrystalline Silica)

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