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Radiolite opal is a rare variety of opal formed through the silicification of ancient marine organisms called radiolarians, creating a distinctive fossil-bearing precious gemstone with microscopic skeletal remains preserved in opaline silica. The stone exhibits a unique internal structure where the calcium carbonate shells of prehistoric radiolarians have been replaced by silica while maintaining their original geometric patterns and lattice-like frameworks.
The gemstone forms in marine sedimentary deposits where radiolarian fossils accumulated during the Mesozoic era. These deposits underwent diagenesis, transforming the biogenic silica into precious opal while preserving the intricate microscopic structures of the radiolarian tests. The resulting stone displays both play-of-color and preserved fossil patterns, making it valuable to both gemologists and paleontologists.
The optical properties of radiolite opal include translucency to opacity, with color variations ranging from white to gray, often showing spectral colors through its characteristic opalescence. The preserved radiolarian fossils create distinctive geometric patterns visible under magnification, differentiating it from common opal varieties.
Radiolite opal is typically a natural gemstone.
Common names for Radiolite opal include diatomite opal, diatomaceous earth opal, and fossilized algae opal.
Radiolite opal, similar to other opals, typically has a hardness of about 5.5 to 6.5 on the Mohs scale. This makes it relatively softer compared to many other gemstones, and susceptible to scratches and abrasion.
The refractive index of radiolite opal generally ranges from approximately 1.44 to 1.46, which is somewhat lower than many other gemstones.
Radiolite opal exhibits a distinctive subvitreous to waxy luster, which contributes to its unique visual appeal.
Opals, including radiolite opal, do not have any cleavage. This means they do not break along any defined plane.
The fracture of radiolite opal is typically conchoidal, which means it breaks with a smooth curved surface, similar to the way glass breaks.
The specific gravity for radiolite opal is generally around 2.1, which is considered relatively light among gemstones.
Radiolite opal is amorphous and does not have a crystalline structure, hence it shows no double refraction (birefringence).
Opals are well-known for their “”play-of-color”” or fire, and radiolite opal is no exception. This optical phenomenon is due to the diffraction of light passing through tiny silica spheres within the structure of the opal.
Being an amorphous mineraloid, radiolite opal does not belong to any crystal system.
Radiolite opal can display a wide range of colors, often showing vibrant play-of-color effects against a white or light body color.
Radiolite opal ranges from opaque to translucent. The level of transparency can affect the value and aesthetic of the gemstone.
Pleochroism is not applicable to radiolite opal since it is amorphous and does not have a crystalline structure to exhibit color variation based on crystallographic orientation.
Some opals, including radiolite opal, may exhibit fluorescence under ultraviolet light, typically showing a white or greenish glow.
Opal is generally considered to have fair to good toughness, but it can be prone to cracking or “”crazing”” under extreme temperature changes, dehydration, or physical stress.
Radiolite opal is brittle, which means it can easily break or chip upon impact.
As an amorphous gemstone, radiolite opal does not have an optic sign.
Radiolite opal does not typically display a characteristic absorption spectrum due to its amorphous nature.
Opals, including radiolite opal, are composed of hydrated silica (SiO2·nH2O).
While typically noted for its play-of-color, some radiolite opals may exhibit chatoyancy when cut appropriately and when fibrous inclusions are present.
Radiolite opal does not generally display asterism. This effect is more commonly associated with other gemstones like sapphire and ruby which have suitable crystal structures and inclusions.
The iridescence or play-of-color in radiolite opal is one of its most defining and sought-after features, caused by the diffraction of light through its internal structure.
Radiolite opal is not magnetic.
As a type of opal, radiolite opal is generally an insulator with very low electrical conductivity.
Radiolite opal is not radioactive.
