gemstone

Polished fire agate

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

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; brown to reddish-orange body with likely iridescent red flashes, waxy-to-vitreous luster, cryptocrystalline structure, and no visible cleavage. The rounded shape and glossy surface indicate polishing.

Identified August 30, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, commonly with layered limonite/goethite inclusions that create fire. Most commercial fire agate formed in Tertiary volcanic terrains roughly 20–40 million years ago.

Uses & applications

Used primarily as a cabochon gemstone, pendant, or collector specimen; it has little industrial or construction use. Value depends strongly on brightness, coverage, pattern, and polish quality.

Geological facts

Its “fire” is structural iridescence caused by light interference through thin, curved layers of iron oxides and chalcedony—not actual opal-like play-of-color. Strong fire is usually visible only under directional light and when viewed at specific angles.

Field identification & locations

Identify by testing for quartz-like hardness, dense chalcedony texture, iron-rich brown-red color, and angle-dependent flashes beneath the surface; common sources include Arizona, Mexico, and parts of the southwestern United States. A gemological test is needed to distinguish it from dyed agate or glass.