gemstone

Fire Opal

Hydrated amorphous silica (SiO2·nH2O)

Hardness: 5.5 to 6.5 on the Mohs scale; Color: Red, orange, yellow, brown with play-of-color; Luster: Vitreous to sub-vitreous; Crystal Structure: Amorphous (non-crystalline, silica spheres); Cleavage: None; Specific Gravity: 1.98 to 2.20

Hardness: 5
Color: Red, orange, yellow, brown with play-of-color
Luster: Vitreous to sub-vitreous

Identified August 3, 2026More gemstone →

Explore Fire Opal in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed from a solution of silica and water, often in volcanic environments where silica-rich water seeps into cavities and cracks in rocks, solidifying over millions of years.

Uses & applications

Used primarily in fine jewelry such as rings, pendants, and earrings; highly valued by gemstone collectors and lapidaries.

Geological facts

Fire opals are unique among opals because they often exhibit bright body colors with or without the characteristic play-of-color. Mexico is one of the most famous producers of fine fire opals.

Field identification & locations

Can be identified by its warm body color and vitreous luster when polished. Often found in volcanic regions and associated with rhyolite or basalt deposits.