Green Opal
Amorphous Hydrous Silica (Opal var. Green) · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Amorphous (Non-crystalline); typically occurs in massive, botryoidal, or reniform habits with no defined internal structure.
Mineral Group
Silicates (Tectosilicate / Mineraloid)
Chemical Formula
SiO2 · nH2O (Silica with variable water content and Nickel or Iron impurities)
Formation Process
Sedimentary/Hydrothermal: Forms at relatively low temperatures from silica-rich waters circulating through rock fractures or cavities, often as a result of chemical weathering.
About This Crystal
An opaque to translucent lime-to-olive green specimen with a distinct waxy to resinous luster. The sample shows a massive habit with smooth, slightly rounded surfaces and lacks the 'play of color' found in precious opal, classifying it as 'common opal'.
Physical Characteristics
Color: Pale green to olive green; Streak: White; Cleavage: None; Fracture: Conchoidal to uneven; Specific Gravity: 1.9–2.3; Fluorescence: Often inert but can show weak green or yellow under UV.
Optical Properties
Isotropic (Singly refractive); Refractive Index: 1.42–1.47; No pleochroism or birefringence; Lacks play-of-color (opalescence) but may show light scattering.
Hardness & Durability
Origin Region
Madagascar, Tanzania, Serbia, Australia, and Brazil. Common in weathered ultramafic rocks or volcanic ash beds.
Hardness & Durability
Mohs Hardness: 5.5 to 6.5. Relatively brittle with low toughness; sensitive to sudden temperature changes and physical impact.
Care & Maintenance
Avoid ultrasonic cleaners and steamers; clean with warm soapy water and a soft cloth. Store in a humid environment if possible or away from direct heat to prevent dehydration and cracking (crazing).
Rarity & Value
Common. Generally affordable. Value is determined by color intensity and size. It is rarely treated but sometimes dyed to enhance green saturation.
Special Characteristics
As a 'Common Opal', its primary appeal is its 'jelly-like' or waxy consistency and soothing natural green hue. It does not exhibit the flashes of light seen in precious opal.
Lore & History
Historically used as decorative stones. In metaphysical traditions, it is associated with the Heart Chakra and believed to assist in emotional recovery and strengthening relationships. Ancient Greek lore often associated opals with the tears of Zeus.