sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Brown, tan, and purple/red bands; Luster: Dull to waxy; Texture: Fine-grained, cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs scale
Color: Brown, tan, and purple/red bands
Luster: Dull to waxy

Identified July 16, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Brown, tan, and purple/red bands; Luster: Dull to waxy; Texture: Fine-grained, cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed primarily as a chemical sedimentary rock through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments. The banding represents variations in mineral impurities (like iron oxides) during deposition.

Uses & applications

Historically used for stone tools due to its sharp conchoidal fracture. Modernly used in landscaping, as a decorative lapidary material, and occasionally for industrial abrasives.

Geological facts

Chert is so durable that it can survive long periods of weathering, often found as pebbles in stream beds long after the surrounding rock has eroded away. Banded varieties are often called 'ribbon chert'.

Field identification & locations

Identify by its hardness (will scratch glass), waxy luster on fresh surfaces, and smooth, curved (conchoidal) fracture lines. Commonly found in sedimentary basins and oceanic crust sequences.