mineral

White Opal

Hydrated Silica (SiO2·nH2O)

Hardness: 5.5-6.5 Mohs. Color: Milky white with varying degrees of translucency. Luster: Subvitreous to waxy. Crystal structure: Amorphous (non-crystalline). Cleavage: None. Specific gravity: 1.9-2.3.

Hardness: 5
Color: Milky white with varying degrees of translucency
Luster: Subvitreous to waxy

Identified June 12, 2026More mineral →

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Physical properties

Formation & geological history

Formed from the deposition of silica-rich water in crevices or voids within sedimentary or volcanic rocks. It typically forms at relatively low temperatures over millions of years.

Uses & applications

Primarily used in jewelry as gemstones (cabochons), and highly valued as mineral specimens by collectors. Low-grade opal can be used as an abrasive or in ceramics.

Geological facts

Opal is a mineraloid because it does not have a crystalline structure. It contains between 3% and 21% water by weight. Known as the birthstone for October.

Field identification & locations

Identify in the field by its waxy luster, conchoidal fracture (curved breaks), and lack of crystal faces. It is commonly found in Australia, Ethiopia, and the Western USA. Look for milky, translucent nodules in basalt or sandstone seams.