gemstone

Red-and-gray banded agate

Chalcedony (microcrystalline quartz), SiO₂, with iron-oxide coloration

AI-generated identification · may be incorrect

Typically hardness 6.5–7 Mohs, waxy to vitreous luster, translucent edges, and curved or parallel banding; no visible cleavage, conchoidal fracture, and specific gravity around 2.60–2.65. The red color is commonly caused by hematite or other iron oxides, while gray bands reflect impurities or differing silica textures.

Identified August 30, 2026More gemstone →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater repeatedly fills cavities in volcanic rock, depositing concentric or rhythmic chalcedony layers. It is generally Cenozoic to older, with age depending on the host volcanic formation.

Uses & applications

Used for cabochons, beads, carvings, bookends, and polished collectibles; lesser material is used for decorative stone and abrasives.

Geological facts

The specimen appears tumbled or naturally water-worn, with vivid red-orange bands and a gray-white central zone. Agate is a variety of chalcedony rather than a separate mineral species.

Field identification & locations

Identify by its fine banding, lack of cleavage, waxy surface, and inability to scratch with a steel knife easily; common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the western United States. Acid testing is unnecessary; a glass-scratch test can help but may damage the specimen.