mineral

Fire Agate

Silicon Dioxide (SiO2) with layers of Limonite/Goethite

Hardness: 6.5-7 Mohs; Color: Brown, reddish-orange with iridescent flashes; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Brown, reddish-orange with iridescent flashes
Luster: Vitreous to waxy

Identified June 3, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, reddish-orange with iridescent flashes; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Specific Gravity: 2.58-2.64

Formation & geological history

Formed through volcanic activity in the Tertiary period. Hot water saturated with silica and iron oxide filled cavities in volcanic rock, cooling to form botryoidal layers that create an interference of light (iridescence).

Uses & applications

Primarily used in jewelry as cabochons, for wire wrapping, and as unique collector specimens.

Geological facts

The 'fire' effect is not caused by mineral inclusions but by a diffraction effect known as the Schiller effect, caused by alternating layers of silica and iron oxide. Only found in the southwestern US and northern Mexico.

Field identification & locations

Identify by its characteristic brown-red stone base and thin, iridescent 'bubbles' or layers when tilted in light. Found primarily in Arizona, California, and Mexico. Collectors should look for vibrant multi-color play.

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Biotite Schist

Biotite-rich Schist [K(Mg,Fe)3AlSi3O10(F,OH)2]

metamorphic