sedimentary

Banded Chert (River Pebble)

Microcrystalline Quartz (SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Cream, tan, and reddish-brown bands; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.91

Hardness: 6
Color: Cream, tan, and reddish-brown bands
Luster: Waxy to vitreous

Identified March 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine or lacustrine environments. This specific specimen has been tumbled and rounded by water action in a river or beach setting. Geological age varies widely from Precambrian to Cenozoic.

Uses & applications

Commonly used in lapidary work for cabochons or tumbling. Historically used for stone tools (arrowheads/scrapers) due to its sharp conchoidal fracture. Industrially used as an abrasive or in decorative landscaping.

Geological facts

Banded chert is often formed from the remains of diatoms or radiolarians. The distinct reddish bands in this specimen suggest the presence of iron oxide (hematite) impurities during the mineralization process.

Field identification & locations

Identify in the field by its hardness (will scratch glass), waxy feel, and smooth water-worn surface. It is frequently found in riverbeds, gravel pits, and glacial till. Collectors look for unique banding patterns for rock tumbling.

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