mineral

Tumbled banded agate (likely carnelian or sardonyx)

Microcrystalline quartz, SiO₂ (chalcedony with iron-oxide banding)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; reddish-brown to burgundy bands, waxy-to-glassy luster, cryptocrystalline structure, no visible cleavage, and specific gravity about 2.6. The smooth glossy surface indicates tumbling and polishing.

Identified August 26, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing successive chalcedony layers; iron produces the red-brown color. Individual agates may range from Paleozoic to recent, depending on the host volcanic rock.

Uses & applications

Used for cabochons, beads, carvings, ornaments, and inexpensive jewelry; polished pieces are popular collector specimens.

Geological facts

Banded agate is a variety of chalcedony rather than a separate mineral species. Strong parallel or curved banding and translucency are key diagnostic features.

Field identification & locations

Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the United States. Inspect translucency, curved bands, and hardness; glass imitations may show bubbles and scratch more easily.