gemstone

Cantera Opal (Mexican Fire Opal in Rhyolite)

Hydrated silicon dioxide in rhyolitic volcanic matrix (SiO2·nH2O)

AI-generated identification · may be incorrect

Hardness 5.5 - 6.5 (opal) / ~6-7 (matrix); Color: brownish-red to tan vesicular matrix with pockets of translucent to play-of-color precious/jelly opal; Vitreous to waxy luster on opal pockets, dull on raw matrix; Amorphous structure (opal); Specific gravity 2.1 - 2.3.

Identified October 3, 2026More gemstone →

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Physical properties

Formation & geological history

Formed through volcanic activity where silica-rich waters percolated into gas cavities and vesicles of cooling rhyolite lavas, gradually depositing opal within the cavities during the Tertiary period.

Uses & applications

Popular lapidary material polished into ornamental shapes such as cabochons, spheres, and carved polished eggs; widely collected as a unique gem display piece.

Geological facts

The word 'Cantera' means 'quarry' in Spanish, referring to the porous volcanic quarry rock matrix that naturally holds these gem opal deposits. A small speck of play-of-color (green/red flash) is visible near the upper-middle section.

Field identification & locations

Distinctive mottled red/brown rhyolite matrix containing glossy inclusions of translucent jelly or fire opal. Almost exclusively sourced from Magdalena, Jalisco, and Querétaro, Mexico.