mineral

Fire Agate

Agate (Variety of Chalcedony), SiO2 (Silicon Dioxide)

Hardness: 6.5-7 (Mohs scale); Color: Brown base with iridescent flashes of orange, red, green, and gold; Luster: Waxy to vitreous; Crystal Structure: Trigonal (Cryptocrystalline); Cleavage: None; Specific Gravity: 2.58-2.64

Hardness: 6
Luster: Waxy to vitreous

Identified June 16, 2026More mineral →

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Physical properties

Formation & geological history

Formed during the Tertiary period (roughly 24-36 million years ago) through volcanic activity. Hot water saturated with silica and iron oxide seeped into cracks and bubbles in volcanic rocks, depositing thin layers of chalcedony that create an interference effect.

Uses & applications

Primarily used in high-quality jewelry such as rings, pendants, and carvings. Also highly valued as a collector's mineral due to its unique optical properties.

Geological facts

The 'fire' or iridescence is caused by the Schiller effect, where light is diffraction-grated by alternating thin layers of iron oxide (limonite or goethite) and silica. Famous deposits are restricted primarily to the Southwestern USA and Northern Mexico.

Field identification & locations

Identify by its botryoidal (grape-like) growth habit and distinctive flashes of color inside a brown or reddish chalcedony matrix. Commonly found in desert regions of Arizona, California, and Mexico. Collectors look for high color intensity and 'play of light'.

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