gemstone

Polished agate-bearing rock

Chalcedony (microcrystalline quartz, SiO₂) with iron-oxide inclusions; likely agate in host rock

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray-brown, orange, and black banding with a waxy to vitreous luster. Quartz is trigonal and has no cleavage; orange zones likely iron-stained chalcedony, while the dark matrix may be volcanic or altered host rock.

Identified September 6, 2026More gemstone →

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Physical properties

Formation & geological history

Formed when silica-rich fluids filled cavities or fractures in volcanic rock, depositing layered chalcedony over time; the exact geological age cannot be determined from the image. Agates commonly form in basaltic lava flows and volcanic cavities.

Uses & applications

Used as a lapidary specimen, cabochon, ornamental stone, and collector’s piece; quality depends on pattern, color, polish, and completeness of the banding.

Geological facts

The orange color commonly results from hematite or goethite. Agate is a cryptocrystalline variety of quartz whose bands may record repeated changes in fluid chemistry.

Field identification & locations

Identify by its translucency, curved or irregular banding, waxy polish, and ability to scratch glass; a steel blade usually does not scratch it. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.