sedimentary

Banded chert (likely jasper/chalcedony)

Microcrystalline quartz (SiO₂), chiefly chert with iron-oxide staining

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque cream, gray, tan, and reddish-brown bands with a dull to waxy or subtly vitreous luster. It has cryptocrystalline quartz, no visible cleavage, conchoidal fracture, and typical specific gravity near 2.6.

Identified September 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater or marine silica replaces or cements sediment, commonly with later iron-oxide staining and brecciation; ages range from Precambrian to recent. The specimen appears naturally weathered and possibly smoothed by water.

Uses & applications

Used for flaking tools, aggregate, decorative stone, cabochons, and lapidary carvings; attractive patterned pieces are collectible but generally inexpensive.

Geological facts

Chert can produce extremely sharp edges when fractured. The reddish colors usually reflect hematite or other iron oxides, while gray and cream zones are silica-rich.

Field identification & locations

Identify by its very hard, dense body, waxy surface, conchoidal fracture, and inability to scratch it with a steel knife; it should not fizz with dilute hydrochloric acid. Common in sedimentary formations, river gravels, and silica-rich replacement deposits worldwide.