Hyalite Opal
Opal-AN (Amorphous-Network) · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Amorphous (Non-crystalline); typically occurs in botryoidal, crust-like, or globular habits.
Mineral Group
Silicates (Subgroup: Tectosilicates)
Chemical Formula
SiO2·nH2O
Formation Process
Hydrothermal; it forms from the deposition of silica-rich fluids at relatively low temperatures, often in volcanic cavities, fissures, or as secondary coatings on other rocks.
About This Crystal
A colorless, transparent to translucent variety of opal. It lacks the internal 'play-of-color' seen in precious opal, appearing instead like a coating of water droplets or melted glass with a vitreous to resinous luster.
Physical Characteristics
Color: Colorless, white, or pale yellow; Streak: White; Cleavage: None; Fracture: Conchoidal; Specific Gravity: 1.9–2.1; Tenacity: Brittle; Fluorescence: Often exhibits strong green fluorescence under UV light due to trace uranium impurities.
Optical Properties
Refractive Index: 1.44–1.46 (Isotropic); Birefringence: None; Dispersion: Low; Phenomenon: Adularescence-like glow when uranium-bearing specimens are exposed to UV rays.
Hardness & Durability
Origin Region
Globally distributed; notable sources include Mexico (Zacatecas), Namibia, Czech Republic, and various volcanic regions in the USA like Oregon.
Hardness & Durability
Mohs Hardness: 5.5–6.0; Toughness: Poor; Stability: Sensitive to sudden temperature changes and dehydration, which can cause cracking (crazing).
Care & Maintenance
Clean with warm soapy water and a soft brush. Avoid ultrasonic cleaners, steam, and harsh chemicals. Store in a stable environment away from direct heat or intense sunlight to prevent dehydration.
Rarity & Value
Relatively common in crust form, but high-clarity specimens or those showing intense neon-green fluorescence are highly sought after by collectors. Value ranges from a few dollars for small crusts to hundreds for large, fluorescent display pieces.
Special Characteristics
Daylight fluorescence (in rare cases) and intense shortwave/longwave UV fluorescence. It is unique for its resemblance to glass or water droplets ('Hyalite' is derived from the Greek word for glass).
Lore & History
Historically used as a novelty mineral specimen for its glass-like appearance. In metaphysical folklore, it is associated with clarity of mind, emotional balance, and the 'water element' due to its fluid-like growth patterns.