mineral

Tumbled agate or chalcedony nodule

Microcrystalline quartz (SiO₂), likely agate/chalcedony with iron-oxide staining

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent brown, cream, and gray banding with a waxy-to-glassy luster. Cryptocrystalline quartz lacks visible individual crystals; the cavity appears lined with tiny druzy quartz crystals.

Identified August 28, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing concentric chalcedony bands and later quartz. Such nodules commonly formed during ancient volcanic episodes, though the exact age cannot be determined from the image.

Uses & applications

Used as an ornamental and lapidary material for cabochons, carvings, beads, and polished specimens; cavity-bearing pieces are popular mineral collectibles.

Geological facts

The visible banding and sparkling cavity strongly suggest an agate geode or thunderegg fragment rather than ordinary jasper. Brown coloration commonly results from iron oxides.

Field identification & locations

Identify by curved parallel bands, translucency, very high hardness, and resistance to scratching by steel; it should scratch glass but not be scratched by a steel knife. Common sources include Brazil, Uruguay, Mexico, Madagascar, and the western United States.