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Wax opal is a distinctive variety of common opal exhibiting a waxy luster and translucent to opaque appearance, characterized by its resinous sheen and microscopic spherical silica structure. The mineral forms through low-temperature hydrothermal processes, where silica-rich solutions deposit within rock cavities under specific geological conditions.
This mineraloid contains 6-10% water content within its amorphous silica framework, contributing to its unique optical properties and waxy surface texture. Wax opal displays colors ranging from white to yellow, brown, and occasionally green, derived from trace elements and mineral inclusions. Its formation occurs primarily in volcanic regions, often associated with weathered basalt deposits and sedimentary environments.
The material’s distinctive properties stem from its internal structure of closely packed silica spheres, typically 150-300 nanometers in diameter, arranged in a non-crystalline pattern. Unlike precious opal, wax opal lacks play-of-color due to its irregular sphere sizes and arrangement, resulting in its characteristic waxy appearance valued in lapidary arts and mineralogical collections.
Wax opal is typically a natural gemstone.
Common names for Wax opal include: Menilite, Liver Opal, and Wood Opal.
Wax opal has a hardness rating of approximately 5.5 to 6.5 on the Mohs scale. This makes it relatively softer compared to many other gemstones, which means it can be susceptible to scratches and abrasions.
The refractive index of wax opal typically ranges from about 1.44 to 1.46. This property helps in determining how much the light is bent or refracted when entering the stone.
Wax opal exhibits a distinctive waxy luster, which gives the gemstone a soft glow. This characteristic luster differentiates it from other types of opals which may have a more vitreous (glass-like) appearance.
Opals, including wax opal, generally do not exhibit cleavage. This means that they do not have natural planes of weakness along which they can split easily.
Wax opal typically has a conchoidal to uneven fracture pattern, which is common among opals. This fracture type results in smooth, curved surfaces on the broken edges.
The specific gravity of wax opal generally ranges from about 1.98 to 2.20, which is considered average among gemstones.
Wax opal is an isotropic material, meaning it has a single refractive index and does not exhibit double refraction or birefringence under polarized light.
Wax opal has relatively low dispersion compared to other opals, contributing to its subdued fire or the play of color typically seen in other opal varieties.
Opals, including wax opals, are amorphous and do not have a crystalline structure. They are made of silica spheres arranged in a random pattern.
Wax opal predominantly exhibits pale to rich yellow or brown colors. It might also show subtle color plays under certain lighting conditions, but these are generally not as vivid as those seen in precious opals.
Wax opal ranges from opaque to translucent. Its waxy appearance can sometimes give it a slightly transparent to semi-transparent look.
Being isotropic, wax opal does not show pleochroism. This means it maintains the same color intensity from all viewing angles.
Wax opal may show weak fluorescence under ultraviolet light, typically green or white, but this can vary depending on the individual specimen.
Wax opal has fair to good toughness, making it relatively resistant to breaking and chipping compared to other more brittle gemstones.
The tenacity of wax opal is generally brittle, which is a common characteristic of opals due to their internal structure and water content.
As an isotropic gemstone, wax opal has an optic sign of uniaxial negative. This describes the optical behavior under polarized light.
Wax opal does not have a characteristic absorption spectrum due to its amorphous nature and isotropic properties.
Wax opal is primarily composed of silica (SiO2) and water. The water content can vary but typically ranges between 3% and 10% by weight.
While not common, some wax opals can exhibit a weak cat’s eye effect, where a band of light moves across the stone, depending on the cut and inclusions.
Asterism or the star effect is not typically observed in wax opal due to its isotropic and amorphous nature.
Although not as pronounced as in precious opals, wax opal can exhibit a mild iridescence due to the scattering of light by its microscopic internal structure.
Wax opal shows no magnetism.
Wax opal is generally a poor conductor of electricity, consistent with most non-metallic minerals.
Wax opal is not radioactive and poses no health risks associated with radioactivity.
