mineral

White Opal (Common)

Hydrated Silica (SiO2·nH2O)

Hardness: 5.5-6.5 (Mohs scale); Color: Creamy white to pale gray; Luster: Waxy to vitreous; Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 1.9-2.3

Hardness: 5
Color: Creamy white to pale gray
Luster: Waxy to vitreous

Identified March 28, 2026More mineral →

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Physical properties

Hardness: 5.5-6.5 (Mohs scale); Color: Creamy white to pale gray; Luster: Waxy to vitreous; Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 1.9-2.3

Formation & geological history

Formed from silica-rich water seeping into cracks and cavities in sedimentary or volcanic rock layers. Over millions of years, the water evaporates, leaving behind hardened silica spheres. They are found in strata ranging from the Cretaceous to the Tertiary periods.

Uses & applications

Used in gemstone jewelry (cabochons), as an abrasive in polishing agents, in the production of cosmetics, and as a popular specimen for mineral collectors.

Geological facts

Unlike 'Precious Opal,' common opal (often called 'potch') lacks play-of-color because its internal silica spheres are disorganized in size and arrangement. It is technically a mineraloid rather than a mineral due to its lack of a crystal structure.

Field identification & locations

Identify in the field by its characteristic waxy luster, smooth conchoidal (shell-like) fractures, and its light weight relative to quartz. Commonly found in Australia (Coober Pedy), Ethiopia, and the Western United States (Nevada and Oregon).