gemstone

Polished brown agate (likely carnelian/chalcedony)

Microcrystalline quartz, SiO₂; chalcedony with iron-oxide coloration

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; brown to reddish-brown, waxy to vitreous luster, cryptocrystalline structure, no visible cleavage, specific gravity about 2.6. The rounded, glossy form appears polished or carved rather than naturally exposed.

Identified September 3, 2026More gemstone →

Explore Polished brown agate (likely carnelian/chalcedony) in the encyclopedia →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing chalcedony in bands or layers; coloration comes from iron oxides. Most examples are Cenozoic to older, depending on locality.

Uses & applications

Used for cabochons, carvings, beads, ornaments, and lapidary specimens; durable but less valuable than transparent quartz gems.

Geological facts

Agate is a variety of chalcedony, and “carnelian” refers to orange-red iron-colored chalcedony. The image alone cannot confirm banding or distinguish natural agate from dyed chalcedony.

Field identification & locations

Identify by its waxy luster, glass-like hardness, lack of cleavage, and conchoidal fracture; it commonly occurs in volcanic cavities in Brazil, Uruguay, India, Madagascar, and the United States.