sedimentary

Banded Chert (with Quartz Vein)

Microcrystalline Silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale); Color: Dark grey to black matrix with white bands; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Hardness: 6
Color: Dark grey to black matrix with white bands
Luster: Dull to waxy

Identified April 7, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Dark grey to black matrix with white bands; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians) or chemical precipitation in marine environments. The white bands are secondary quartz veins formed when silica-rich fluids filled cracks in the host rock over millions of years.

Uses & applications

Used historically for stone tools due to its sharp edges; today used for decorative garden stones, tumbling, and occasionally in jewelry as ornemental stones.

Geological facts

Chert is so hard it can scratch steel and was used by prehistoric humans to start fires when struck against iron or steel, creating sparks.

Field identification & locations

Identify by its extreme hardness and smooth, waxy surface when polished. Commonly found on beaches or in riverbeds where water has rounded the stone. Can be found globally in limestone and chalk formations.