gemstone

Cantera Opal (Mexican Fire Opal in Rhyolite Matrix)

Hydrated amorphous silica in rhyolite (SiO2·nH2O in volcanic matrix)

AI-generated identification · may be incorrect

Hardness: 5.5 - 6.5 (opal) and ~6 - 7 (rhyolitic matrix); Color: translucent to transparent amber, orange, yellow, and clear precious opal with play-of-color flashes in a pinkish-tan to reddish-brown rhyolite matrix; Luster: vitreous to resinous; Crystal structure: amorphous (mineraloid); Specific gravity: ~2.1 - 2.6.

Hardness: 5
Luster: vitreous to resinous

Identified October 3, 2026More gemstone →

Explore Cantera Opal (Mexican Fire Opal in Rhyolite Matrix) in the encyclopedia →

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Physical properties

Formation & geological history

Formed in cavities (vesicles) of volcanic extrusive igneous rock (rhyolite). Silica-rich hydrothermal waters percolated through cooling lava gas pockets, depositing opal nodules within the rock matrix over millions of years (typically Tertiary age).

Uses & applications

Prized in lapidary arts for carving into spheres, cabochons, and decorative ornamental items, as well as high-end collectors' specimens and artisan jewelry.

Geological facts

'Cantera' translates to 'quarry' in Spanish, referring to the porous volcanic stone quarry matrix. Unlike many treated composites, high-end Cantera opal spheres are carved directly from solid volcanic boulders containing natural opal pockets.

Field identification & locations

Identified by precious opal pockets embedded within a fine-grained, pinkish-brown to reddish volcanic matrix. Prominently found in Magdalena, Jalisco, and Querétaro, Mexico. Collectors prize spheres with vibrant play-of-color flashes visible across multiple distinct pockets.