sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Red, brown, and tan banding; Luster: Waxy to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 6
Color: Red, brown, and tan banding
Luster: Waxy to dull

Identified June 13, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Red, brown, and tan banding; Luster: Waxy to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed via the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from silica-rich fluids in marine environments. Banding often reflects pulses of sediment deposition or chemical changes during formation.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Today used as an ornamental stone, for lapidary work (cabochons), and as a collector's specimen.

Geological facts

The red colors in this specimen are likely caused by iron oxide impurities (Hematite). Chert is so hard it can strike sparks from steel, which is why it was often used in flintlock firearms.

Field identification & locations

Identify by its hardness (will scratch glass), waxy appearance, and smooth, curved (conchoidal) breaks. Look for it in sedimentary basins, riverbeds, and as nodules within limestone or dolostone formations.