mineral

Common Opal

Hydrated amorphous form of silica (SiO2·nH2O)

Hardness: 5.5-6.5 (Mohs scale), Color: Milky white to light blue, Luster: Vitreous to waxy, Crystal Structure: Amorphous (non-crystalline), Fracture: Conchoidal, Specific Gravity: 1.9-2.3

Hardness: 5

Identified April 6, 2026More mineral →

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Physical properties

Hardness: 5.5-6.5 (Mohs scale), Color: Milky white to light blue, Luster: Vitreous to waxy, Crystal Structure: Amorphous (non-crystalline), Fracture: Conchoidal, Specific Gravity: 1.9-2.3

Formation & geological history

Formed from the precipitation of silica-rich water in the cracks and cavities of sedimentary or volcanic rocks. It is usually found in areas with ancient geothermal activity or heavy weathering.

Uses & applications

Used primarily in jewelry as cabochons or beads, as ornamental stone, and is highly sought after by mineral collectors for its unique translucency.

Geological facts

Unlike precious opal, common opal does not exhibit play-of-color or opalescence. It can occur in nearly any color and often forms the matrix for more valuable opal layers.

Field identification & locations

Identify by its characteristic waxy luster and conchoidal fracture (curved, glass-like breaks). Common in Australia, Mexico, and the Western United States (Nevada/Oregon).

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