Green Opal (Common Opal)
Amorphous Hydrous Silica var. Common Opal · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Amorphous (Non-crystalline). Typically occurs in massive form, botryoidal crusts, or as replacement material in fossils.
Mineral Group
Silicates (Tectosilicate class, though technically a mineraloid)
Chemical Formula
SiO2·nH2O (Contains trace nickel, iron, or chromium which contributes to the green hue)
Formation Process
Sedimentary/Hydrothermal. Forms at low temperatures from silica-rich waters that seep into rock cavities and solidify over long periods.
About This Crystal
An opaque to translucent lime-green or olive-green mass. It exhibits a waxy to resinous luster and lacks the 'play-of-color' seen in precious opal. This specimen shows a rough, chunky texture with visible conchoidal fracture scars.
Physical Characteristics
Color: Green to yellowish-green; Streak: White; Cleavage: None; Fracture: Conchoidal (shell-like); Specific Gravity: 1.9–2.3; Fluorescence: Often glows neon green under shortwave UV due to trace uranium ions.
Optical Properties
Refractive Index: 1.42–1.47; Isotropic (singly refractive); Lacks pleochroism and dispersion; Exhibits opalescence in some varieties but mostly waxy sheen in this form.
Hardness & Durability
Origin Region
Madagascar, Tanzania, Peru, and Australia. Often found in weathered volcanic rocks or altered ultramafic environments.
Hardness & Durability
Mohs Hardness: 5.5 to 6.0; Toughness: Very brittle; Stability: Sensitive to heat and dehydration which can cause 'crazing' or cracking.
Care & Maintenance
Clean with warm soapy water only; No ultrasonic or steam cleaners. Store in a cool place away from direct sunlight or heat sources to prevent dehydration. Occasional moisture exposure can help maintain hydration.
Rarity & Value
Common. Value is determined by color saturation and size. Generally inexpensive as a rough specimen ($2-$10 for small roughs), but higher-grade translucent material is more valuable for lapidary work.
Special Characteristics
Notable for its waxy luster and distinct 'common opal' appearance. Some specimens feature dendritic (plant-like) inclusions of manganese or iron.
Lore & History
Used by various cultures for its vibrant earthy colors. In metaphysical traditions, it is often associated with the heart chakra, believed to provide emotional support and a connection to nature. Historically, opals were seen as symbols of hope and purity.