sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Tan, brown, white, and rust-colored layers; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Tan, brown, white, and rust-colored layers
Luster: Waxy to dull

Identified March 19, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, brown, white, and rust-colored layers; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed by the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or chemical precipitation of silica in ocean or freshwater basins. The banding reflects seasonal or rhythmic changes in sediment deposition.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modern uses include crushed stone for construction, abrasives, and as a decorative stone for jewelry/cabochons.

Geological facts

Banded chert is often associated with Banded Iron Formations (BIFs), which contain some of the oldest evidence of life on Earth (stromatolites). It is highly resistant to weathering, often found as cobbles in riverbeds long after surrounding rock has eroded.

Field identification & locations

Identify in the field by its distinct horizontal layering, extreme hardness (it will scratch glass and steel), and smooth, shell-like (conchoidal) fracture surfaces. Commonly found in limestone outcroppings and rocky riverbanks.