mineral

Fire Agate

Silicon Dioxide (SiO2) with layered Iron Oxide (Limonite/Goethite)

Hardness: 6.5-7.0 (Mohs); Color: Brown base with iridescent flashes of red, orange, and green; Luster: Waxy to vitreous; Crystal structure: Hexagonal (rhombohedral) Cryptocrystalline; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Brown base with iridescent flashes of red, orange, and green
Luster: Waxy to vitreous

Identified May 18, 2026More mineral →

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Physical properties

Formation & geological history

Formed during periods of volcanic activity when hot water saturated with silica and iron oxide crowded into rock cavities, creating thin layers that produce 'Schiller' effect. Primarily Tertiary period.

Uses & applications

Primarily used in high-end jewelry, lapidary arts, and as a collector's gemstone due to its unique optical properties and botryoidal internal structure.

Geological facts

The iridescent colors in fire agate are caused by the diffraction of light as it passes through alternating layers of silica and iron oxide. Unlike opal, it is very durable and light-stable.

Field identification & locations

Found throughout the Southwestern USA (Arizona, California) and Northern Mexico. Identified by its characteristic botryoidal (grape-like) bumps and iridescent internal flashes visible under a polished surface.

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