sedimentary

Banded agate (likely petrified wood or silicified sediment)

Microcrystalline quartz/chalcedony, SiO₂; possible silicified wood

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; cream, tan, brown, and reddish-brown bands with a dull to waxy luster. Agate consists of cryptocrystalline quartz and commonly shows curved or irregular banding; the blocky grain may indicate replacement of wood or another porous material.

Identified September 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Silica-rich groundwater filled or replaced cavities in volcanic rock or organic material, later hardening into chalcedony and quartz. Exact geological age cannot be determined from the image; silicified wood may range from Paleozoic to Cenozoic.

Uses & applications

Used as a lapidary material for cabochons, carvings, bookends, and polished slabs; attractive pieces are collected rather than used structurally.

Geological facts

The contrasting bands result from repeated changes in silica-rich fluid chemistry and impurities such as iron oxides. Brown-red coloration typically reflects hematite or limonite.

Field identification & locations

Look for translucent edges, waxy luster, very fine grain, and hardness sufficient to scratch ordinary glass; iron staining and possible cellular or fibrous textures support silicification. Common sources include Brazil, Uruguay, Mexico, the western United States, and Madagascar.