mineral
Polished banded agate (likely petrified wood)
Microcrystalline quartz (SiO₂); possibly silicified wood
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; golden-yellow, brown, and gray bands with a waxy-to-glassy polish. Quartz has a trigonal crystal structure, but the fine-grained specimen shows no visible crystals or cleavage; identification as petrified wood is uncertain from the image.
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Physical properties
Hardness about 6.5–7 Mohs; golden-yellow, brown, and gray bands with a waxy-to-glassy polish. Quartz has a trigonal crystal structure, but the fine-grained specimen shows no visible crystals or cleavage; identification as petrified wood is uncertain from the image.
Formation & geological history
Silica-rich fluids can deposit successive layers of chalcedony in cavities, or replace buried wood during silicification. These materials form across many geological ages and settings.
Uses & applications
Used as a decorative polished stone, in jewelry and lapidary work, and as a collectible.
Geological facts
Agate is a variety of chalcedony, itself microcrystalline quartz; its bands record changing conditions during silica deposition.
Field identification & locations
Look for hardness near 7, a smooth polish, and distinct translucent-to-opaque bands; petrified wood may retain grain-like patterns. Agates occur worldwide, including Brazil, Uruguay, Mexico, and the western United States.
