mineral

Fire Opal (Common/Precious in Matrix)

Hydrated Silica (SiO2·nH2O)

Hardness: 5.5-6.5 (Mohs); Color: Orange, yellow, or white set in tan rhyolite matrix; Luster: Vitreous to waxy; Structure: Amorphous; Cleavage: None (Conchoidal fracture).

Hardness: 5
Color: Orange, yellow, or white set in tan rhyolite matrix
Luster: Vitreous to waxy

Identified March 14, 2026More mineral →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 5.5-6.5 (Mohs); Color: Orange, yellow, or white set in tan rhyolite matrix; Luster: Vitreous to waxy; Structure: Amorphous; Cleavage: None (Conchoidal fracture).

Formation & geological history

Formed as silica-rich water seeps into cavities of volcanic rocks, typically rhyolite. Most deposits date from the Tertiary period (roughly 20-30 million years ago) specifically in high-altitude volcanic regions.

Uses & applications

Used primarily in the jewelry industry for cabochon cutting, as gemstones for collectors, and as decorative metaphysical specimens.

Geological facts

Unlike other opals, fire opals from Mexico and similar regions are valued specifically for their warm body color rather than just 'play of color'. They are amorphous, meaning they lack a crystal structure.

Field identification & locations

Identify in the field by looking for translucent, jelly-like orange or white nodes embedded in light-colored, porous volcanic rock. Common in Mexico (Querétaro), Ethiopia, and the Western USA.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

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

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral

Epidote

Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)

mineral