mineral

Polished agate geode slice

Banded chalcedony (microcrystalline SiO₂), with a quartz crystal-lined cavity

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; gray and white concentric bands, waxy-to-vitreous luster, trigonal quartz structure, no visible cleavage, and conchoidal fracture. The polished face reveals fine banding and a central druzy cavity.

Identified October 2, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater deposited successive chalcedony layers in a cavity, later allowing quartz crystals to grow inward. Agates form in volcanic and other rock cavities over geological time; this specimen’s precise age and locality cannot be determined from the image.

Uses & applications

Commonly used for display, lapidary craft, bookends, and jewelry; agate is also used for small ornaments and historically for carved seals.

Geological facts

Agate’s distinctive bands record changing conditions as silica precipitated in layers. The white center is likely quartz crystal growth rather than a separate rock layer.

Field identification & locations

Identify by its curved, concentric bands and hard, glassy-to-waxy silica surface; agates occur worldwide, especially in volcanic regions. This is a cut and polished specimen, so the original locality is not apparent.