Opal

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.

Identified on: 4/23/2026

Mode: Standard