mineral

Blue Opal in Matrix

Hydrated Silica (SiO2·nH2O)

Hardness: 5.5-6.5 on Mohs scale; Color: Cyan to deep blue with brown iron-rich host rock; Luster: Vitreous to waxy; Crystal structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 1.9-2.3

Hardness: 5
Color: Cyan to deep blue with brown iron-rich host rock
Luster: Vitreous to waxy

Identified June 25, 2026More mineral →

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Physical properties

Formation & geological history

Formed from silica-rich water seeping into fissures and cavities of volcanic or sedimentary rocks. This specimen is likely 'common opal' (non-iridescent) found in Cenozoic era deposits, often in arid volcanic environments.

Uses & applications

Commonly used for lapidary work such as cabochons, metaphysical collecting, and jewelry. Higher grades are valued as semi-precious gemstones.

Geological facts

Unlike precious opal, blue common opal does not show 'play-of-color.' Its blue hue is often caused by micro-inclusions of other minerals or light scattering. It is the national stone of Peru, which is home to some of the world's most famous blue opal deposits.

Field identification & locations

Identify by its characteristic waxy luster and smooth, shell-like (conchoidal) fracture surfaces within a rough, earthy matrix. Commonly found in Oregon (USA), Peru, and Australia. Collectors should look for vibrant saturation of the blue color.