mineral

Polished brown banded agate (likely carnelian/chalcedony)

Microcrystalline quartz, SiO₂; chalcedony with iron-oxide inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; dark brown, black, and reddish-brown bands with a waxy to glassy luster. Cryptocrystalline quartz has no visible cleavage and conchoidal fracture; apparent layering may be natural agate banding or a polished fragment.

Identified September 3, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and iron oxides in successive bands, commonly during the Cenozoic or older volcanic episodes. Typical sources include Brazil, Uruguay, India, Madagascar, and the western United States.

Uses & applications

Used for cabochons, beads, carvings, ornaments, and lapidary specimens; agate is also used industrially for abrasion-resistant components.

Geological facts

Agate’s bands record repeated changes in fluid chemistry during cavity filling. The dark coloration commonly results from iron and manganese oxides or included mineral material.

Field identification & locations

Identify by its very hard, smooth polished surface, waxy luster, curved/conchoidal edges, and possible translucent banding; it should scratch glass but not be scratched by a steel blade. Exact identification is limited because the specimen is opaque and highly polished.