mineral

Tumbled agate or chalcedony

Microcrystalline quartz (SiO₂), likely yellow-brown chalcedony/agate

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent cream, honey-yellow, and brown coloration with a waxy to dull luster. No visible cleavage, conchoidal fracture, and cryptocrystalline quartz structure; rounded surface indicates tumbling.

Identified August 16, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities or fractures in volcanic rocks, commonly developing iron-oxide staining and occasional banding. Agate formation spans many geological ages, especially in basaltic regions.

Uses & applications

Used as a low-cost ornamental stone, cabochon, bead, paperweight, or collector specimen. Common tumbled pieces typically have modest value.

Geological facts

Agate is technically banded chalcedony; uniformly colored pieces may be called chalcedony rather than agate. The yellow-brown tones commonly result from hydrated iron oxides.

Field identification & locations

Commonly found in volcanic terrains, including Brazil, Uruguay, India, Mexico, Madagascar, and the western United States. Identify by its quartz hardness, waxy appearance, translucency, and lack of cleavage; glass can look similar but is generally less naturally textured.