Green Opal
Amorphous Hydrated Silica (Opal-AN or Opal-CT) · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Amorphous (Non-crystalline); Habit is typically massive, botryoidal, or as nodular masses with no defined crystal faces.
Mineral Group
Silicates (Tectosilicate / Mineraloid)
Chemical Formula
SiO2·nH2O (Silicon Dioxide with localized water content; green color due to Nickel or iron inclusions)
Formation Process
Sedimentary/Hydrothermal; formed from the precipitation of silica-rich waters at relatively low temperatures, often filling cavities in igneous or sedimentary rocks.
About This Crystal
A non-precious variety of opal characterized by a mossy, lime, or olive green hue. It is translucent to opaque with a waxy to resinous luster and a smooth, almost soapy feel. It lacks the 'play-of-color' seen in precious opal.
Physical Characteristics
Color: Pale to dark green; Streak: White; Cleavage: None; Fracture: Conchoidal to uneven; Specific Gravity: 1.9–2.3; Fluorescence: Can show green or yellow under UV light.
Optical Properties
Refractive Index: 1.42–1.47; Single refraction (Isotropic); Pleochroism: None; Lacks opalescence but may show a milky haze.
Hardness & Durability
Origin Region
Madagascar, Tanzania, Brazil, and Serbia; often found in decomposed volcanic rocks and hydrothermal veins.
Hardness & Durability
Mohs Hardness: 5.5 to 6.0; Toughness: Very brittle; sensitive to thermal shock and dehydration cracks (crazing).
Care & Maintenance
Avoid ultrasonic and steam cleaners; clean only with warm soapy water and a soft cloth. Store in a cool, humid environment to prevent cracking; avoid prolonged exposure to direct sunlight and harsh chemicals.
Rarity & Value
Common; relatively inexpensive compared to precious opal. Value is based on color intensity and uniformity. Treatments are rare for this variety, though occasionally dyed.
Special Characteristics
Often contains dendritic (fern-like) inclusions of manganese or iron; lacks 'fire' but possesses a distinctive 'serpentine-like' appearance in raw form.
Lore & History
Historically used in various cultures as a stone of rejuvenation and emotional recovery. In traditional crystal healing practices, it is associated with the Heart Chakra and believed to promote a sense of calm and mental clarity.