mineral

White Precious Opal

Hydrated Silica (SiO2·nH2O)

Hardness: 5.5-6.5 on Mohs scale; Color: Milky white body with 'play-of-color' (iridescence); Luster: Subvitreous to pearly; Crystal structure: Amorphous (non-crystalline); Specific Gravity: 1.9-2.3.

Hardness: 5
Color: Milky white body with 'play-of-color' (iridescence)
Luster: Subvitreous to pearly

Identified March 18, 2026More mineral →

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Physical properties

Hardness: 5.5-6.5 on Mohs scale; Color: Milky white body with 'play-of-color' (iridescence); Luster: Subvitreous to pearly; Crystal structure: Amorphous (non-crystalline); Specific Gravity: 1.9-2.3.

Formation & geological history

Formed from silica-rich water seeping into cracks and cavities in sedimentary or volcanic rock. Over millions of years, the water evaporates, leaving behind silica deposits. Many famous deposits date to the Cretaceous period.

Uses & applications

Primarily used as a gemstone in jewelry (rings, pendants, earrings) and as a high-value collector's specimen.

Geological facts

Unlike most gemstones, opal is a 'mineraloid' because it lacks a crystal structure. Its rainbow flash is caused by regular patterns of microscopic silica spheres refracting light.

Field identification & locations

Identify by its distinctive milky white background with internal flashes of rainbow color. Commonly found in Australia (Coober Pedy), Ethiopia, and Brazil. In the field, look for 'potch' (common opal) which often indicates precious opal is nearby.