gemstone

Tumbled agate or chalcedony

Microcrystalline quartz (SiO₂), likely gray/brown chalcedony with subtle agate banding

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray-brown body with pale internal bands or fractures and a waxy-to-glassy luster. Massive cryptocrystalline structure, no visible cleavage, and typical specific gravity near 2.60.

Identified September 19, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing chalcedony and quartz in successive layers; commonly Cenozoic to older, depending on its host rock. The specimen has been rounded and polished by tumbling.

Uses & applications

Used for inexpensive cabochons, beads, carvings, worry stones, and ornamental objects; valued mainly for pattern, translucency, and polish quality.

Geological facts

Agate is a variety of chalcedony distinguished by banding, though subtle banding may be difficult to see in a small tumbled piece.

Field identification & locations

Identify by its very fine texture, waxy luster, lack of cleavage, and resistance to scratching by steel; glass should not scratch it. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the United States.