sedimentary

Chert (Chalcedony)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Tan, brown, or white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: 2.6-2.65

Hardness: 6
Color: Tan, brown, or white
Luster: Waxy to dull

Identified June 13, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Tan, brown, or white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: 2.6-2.65

Formation & geological history

Forms as nodules or layered deposits through the accumulation of silica-rich fluids in sedimentary environments, often involving siliceous microorganisms like diatoms or radiolarians. May be found in limestone or chalk beds.

Uses & applications

Historically used for stone tools and arrowheads due to sharp edges; currently used for road ballast, lapidary arts, and gem collecting.

Geological facts

Chert is so hard it can strike sparks from steel. Because it breaks with a conchoidal (shell-like) fracture, it was the primary material for the prehistoric 'Stone Age' tool industry.

Field identification & locations

Identify by its waxy appearance and smooth, curved fracture surfaces. It is translucent to opaque; can be found in pebble or cobble form in riverbeds or coastal cliffs.