sedimentary

Chert (Tan/Grey variety)

Microcrystalline or cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, beige, or light grey; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Tan, beige, or light grey
Luster: Waxy to dull

Identified May 21, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, beige, or light grey; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids in sedimentary basins. Often occurs as nodules in carbonate rocks.

Uses & applications

Historically used for stone tools due to sharp edges; currently used as road aggregate, in landscaping, and as a polishing media in rock tumblers.

Geological facts

Chert was a primary material for prehistoric toolmaking globally; when struck against steel, it can produce sparks, though less effectively than flint.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture patterns and ability to scratch glass. Commonly found in limestone and dolomite formations or as river pebbles.