Common Green Opal

Physical Properties

Hardness: 5.5-6.5 on Mohs scale; Color: Yellowish-green to lime green; Luster: Waxy to vitreous; Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 1.9-2.3

Formation & Geological History

Formed from the precipitation of silica-rich waters in cavities of volcanic or sedimentary rocks. It is non-precious because it lacks the internal structure to produce play-of-color. Typically Neogene to Quaternary in age for common varieties.

Uses & Applications

Primarily used for lapidary work, decorative carvings, cabochons for jewelry, and as collector specimens.

Geological Facts

Unlike precious opal, common opal does not show 'fire' or iridescence. The green color is often caused by inclusions of iron or nickel silicate minerals, such as nontronite.

Field Identification & Locations

Identified by its waxy luster, conchoidal fracture (curved glass-like breaks), and relative lightness compared to quartz. Common in Australia, Madagascar, and the Western United States. Rough specimens are best identified by their smooth, waxy feel.

Identified on: 5/13/2026

Mode: Standard