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Jelly opal is a translucent to semi-transparent variety of hydrated silica (SiO2·nH2O) characterized by its distinctive gelatinous appearance and lower specific gravity compared to other opal varieties. The gemstone exhibits a unique internal structure of closely packed silica spheres with interstitial water content ranging from 6-10% by weight.
This rare form of opal occurs primarily in volcanic deposits within Ethiopia’s Welo province, where geological conditions created ideal environments for its formation during the Tertiary period. The stone’s distinctive jellied appearance results from its amorphous microstructure, which differs from precious opal’s ordered arrangement of silica spheres. Unlike common opal, jelly opal can display remarkable hydrophane properties, temporarily becoming more transparent when immersed in water.
The stone exhibits a refractive index between 1.37-1.42 and a hardness of 5.5-6.5 on the Mohs scale. Its color palette ranges from colorless to honey-yellow, with some specimens displaying subtle play-of-color effects under specific lighting conditions.
Jelly Opal is typically a natural gemstone.
Common names for Jelly Opal include Water Opal, Crystal Opal, and Hyalite.
Jelly opal has a hardness of about 5.5 to 6.5 on the Mohs scale, making it relatively soft compared to many other gemstones. This characteristic means it’s more susceptible to scratches and wear.
The refractive index of jelly opal ranges from approximately 1.44 to 1.46. This property helps define how much light is bent when entering the gemstone.
Jelly opal exhibits a waxy to glassy luster, contributing to its unique visual appeal and the way it interacts with light.
Jelly opal typically does not exhibit cleavage, which is the tendency of a mineral to break along specific planes.
This gemstone usually has an uneven or conchoidal fracture, making it brittle and susceptible to chipping upon impact.
The specific gravity of jelly opal ranges from about 1.98 to 2.25, which is relatively low, indicating that the gem is not very dense.
Jelly opal is isotropic, meaning it has no double refraction. Light travels through the stone at the same speed regardless of its path.
Opals, including jelly opal, are known for their play-of-color, which may sometimes be confused with dispersion. However, jelly opal generally has low dispersion.
Jelly opal is amorphous, meaning it does not have a crystalline structure. This characteristic contributes to its unique patterns of color and light reflection.
The color of jelly opal can range from almost clear to a milky or jelly-like appearance, often showing a vibrant play of color that can include shades of green, blue, red, and orange.
Jelly opal ranges from transparent to translucent, contributing to its depth and the stunning visual effect of its color play.
This gemstone does not exhibit pleochroism due to its amorphous structure and isotropic nature.
Jelly opal can sometimes show a greenish or white fluorescence under ultraviolet light, although this is not a consistent trait across all such opals.
Jelly opal has fair to poor toughness due to its brittleness and higher water content, making it more prone to cracking or breaking.
The tenacity of jelly opal is generally brittle, which means it can easily break under stress or impact.
Being isotropic, the optic sign of jelly opal is non-directional, so the gemstone shows the same optical properties in all directions.
Jelly opal does not typically show a distinct absorption spectrum due to its amorphous nature and variability in composition.
Jelly opal is a form of hydrated silicon dioxide (SiO₂·nH₂O). Its water content can vary, which affects its physical properties and appearance.
While not common, some jelly opals may exhibit chatoyancy when cut appropriately and when fibrous inclusions are present.
Asterism is not typically observed in jelly opals due to their amorphous structure and lack of suitable inclusions.
One of the most appealing features of jelly opal is its iridescence, particularly the play-of-color, which is caused by the diffraction of light passing through microscopic silica spheres within the gemstone.
Jelly opal is not magnetic due to its chemical composition and structure.
Jelly opal is generally a poor conductor of electricity, consistent with most non-metallic minerals.
Jelly opal does not exhibit radioactivity; it is safe to handle and wear as jewelry.
