mineral

Opal

Hydrated Amorphous Silica (SiO2·nH2O)

Hardness: 5.5-6.5 (Mohs); Color: White, blue, or translucent with play-of-color; Luster: Vitreous to waxy; Crystal structure: Amorphous; Cleavage: None; Specific Gravity: 1.9-2.3.

Hardness: 5
Color: White, blue, or translucent with play-of-color
Luster: Vitreous to waxy

Identified April 23, 2026More mineral →

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Physical properties

Hardness: 5.5-6.5 (Mohs); Color: White, blue, or translucent with play-of-color; Luster: Vitreous to waxy; Crystal structure: Amorphous; Cleavage: None; Specific Gravity: 1.9-2.3.

Formation & geological history

Formed from seasonal rains that leach silica from sandstone and carry it into deep cracks. As the water evaporates, it leaves behind a silica deposit. This specimen appears to be a water-worn 'jelly' or 'crystal' opal.

Uses & applications

Primarily used as a gemstone for jewelry (rings, pendants) and as a highly prized specimen for mineral collectors.

Geological facts

Opals contain between 3% and 21% water. Australia produces approximately 95% of the world's precious opal, which is the country's national gemstone.

Field identification & locations

Identify by its characteristic play-of-color (opalescence) and its lightweight, slightly soapy feel compared to glass. Often found in sedimentary environments or volcanic rocks.