Tumbled Green Opal
Amorphous Hydrous Silica (Opal var. Common) · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Amorphous (Non-crystalline); typically occurs in massive, botryoidal, or nodular forms without a defined crystal structure.
Mineral Group
Silicates (Tectosilicate class, though technically a mineraloid)
Chemical Formula
SiO2·nH2O
Formation Process
Sedimentary/Hydrothermal: Formed at relatively low temperatures from silica-rich waters that seep into rock cavities, cracks, or between layers of sediment, slowly depositing hydrated silica.
About This Crystal
This specimen is a tumbled common opal featuring a pale yellowish-green body color with waxy luster. It exhibits translucency to opacity with visible tan and brownish bands or patches of 'matrix' or impurities. The surface is smooth and polished with no play-of-color (no opalescence).
Physical Characteristics
Color: Pale green to lime; Streak: White; Luster: Waxy to vitreous; Diaphaneity: Translucent; Specific Gravity: 1.9–2.3; Fracture: Conchoidal to uneven; 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 dispersion; lacks the 'play of color' found in precious opal.
Hardness & Durability
Origin Region
Madagascar, Brazil, Tanzania, and Serbia; found primarily in volcanic and sedimentary environments.
Hardness & Durability
Mohs Hardness: 5.5–6.5; Toughness: Very poor (brittle and prone to cracking/crazing); Stability: Sensitive to heat and sudden temperature changes.
Care & Maintenance
Clean only with warm soapy water and a soft cloth; avoid ultrasonic cleaners and steam. Store away from direct sunlight and heat to prevent dehydration. Keep separate from harder stones like quartz or sapphire to avoid scratches.
Rarity & Value
Common; relatively inexpensive and widely available. Value is determined by color intensity and size. Treatments like dyeing are occasionally seen but this specimen appears natural.
Special Characteristics
Lacks play-of-color, putting it in the 'Common Opal' category. May contain dendritic inclusions or distinct color zoning as seen in the tan-colored banding on the side.
Lore & History
Historically used as a stone of rejuvenation and emotional recovery. In metaphysical traditions, it is associated with the Heart Chakra and believed to promote a sense of calm and perspective. Ancient cultures often viewed opals as symbols of hope and purity.