sedimentary

Banded Chert Pebble

Silicon Dioxide (SiO2) - Microcrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Dark grey to black with brownish-tan quartz/chalcedony veins and banding; Luster: Waxy to sub-vitreous; Structure: Cryptocrystalline/microcrystalline; Cleavage: None, exhibits conchoidal fracture.

Hardness: 6
Luster: Waxy to sub-vitreous

Identified July 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich biogenic sediments (such as radiolarian shells or diatoms) or precipitation from hydrothermal fluids. Stream-tumbled and smoothed in riverbed environments over geological timescales.

Uses & applications

Historically used for stone tools and fire-starting due to its hardness and sharp conchoidal fracturing. Modern usage includes decorative landscaping, aquariums, lapidary polishing, and tumbled rock collections.

Geological facts

Chert is extremely durable and chemically resistant. Black varieties are often called basanite or touchstone, historically used by goldsmiths to test the purity of precious metals by observing the streak color.

Field identification & locations

Identified by its high hardness (scratches glass), waxy luster, smooth rounded pebble shape, and distinct yellowish/tan veining running through a dark matrix. Commonly found along riverbeds, gravel bars, and beaches.