mineral

Polished agate geode nodule

Microcrystalline quartz (SiO₂), chiefly chalcedony; likely an agate-filled geode

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray-blue and white banded interior with a waxy-to-vitreous luster, set in a rough brown rind. Quartz has a trigonal crystal structure, though its crystals are too fine to see; no prominent cleavage.

Identified October 16, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater deposited successive chalcedony bands in a cavity within volcanic rock, likely during the Cenozoic or earlier; the exact age and locality cannot be determined from the image.

Uses & applications

Commonly polished for display and collecting, and used in jewelry, ornaments, and small decorative objects; agate is also used for beads and precision components.

Geological facts

Agate’s bands record changing chemistry and conditions as silica precipitated in layers inside the cavity.

Field identification & locations

The concentric, fine bands and waxy silica surface distinguish agate from many other geode fillings. Agates occur worldwide, especially in volcanic regions; locality labels and natural, unenhanced banding are useful for collectors.