mineral

Polished agate/chalcedony nodule

Microcrystalline quartz (SiO₂), likely translucent gray-green agate or jasperous chalcedony

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; waxy to glassy luster, translucent gray, olive, cream, and brown coloration, with cryptocrystalline quartz and possible faint banding. It appears naturally fractured and partly polished, with no obvious cleavage and a conchoidal fracture tendency.

Identified August 19, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, precipitating successive layers of chalcedony, quartz, and impurities. The specimen’s exact geological age cannot be determined visually; agates commonly form from Paleozoic to Cenozoic volcanic environments.

Uses & applications

Used as ornamental stone, cabochons, carvings, beads, and polishing material; attractive specimens have modest collector value.

Geological facts

The dark patches may reflect iron or manganese oxides, while pale areas may be quartz or weathered host rock. Agate’s fine texture allows a high polish despite its lack of visible large crystals.

Field identification & locations

Look for translucency, waxy luster, conchoidal edges, and curved or irregular internal banding; it should scratch glass but not be scratched by steel. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.