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Claro opal is a transparent to translucent variety of precious opal displaying vivid play-of-color against a clear or colorless background, predominantly found in Mexico’s Queretaro deposits. The stone exhibits a unique optical phenomenon called opalescence, created by the regular arrangement of silica microspheres that diffract light.
The Mexican claro opal forms in volcanic environments where silica-rich solutions infiltrate rhyolitic host rocks. Its clarity ranges from water-clear to slightly cloudy, with some specimens showing distinct color zoning. The refractive index typically measures between 1.37 and 1.42, with a specific gravity of 1.98-2.20. Unlike common opal, claro opal contains 3-10% water content within its amorphous silica structure.
These gems display spectral colors through a process called diffraction, where light waves interact with the ordered array of silica spheres. Premium specimens exhibit broad flash patterns of red, blue, and green, often visible from multiple viewing angles. The term “”claro”” derives from Spanish, meaning “”clear”” or “”bright.
Claro Opal is typically a natural gemstone.
Common names for Claro Opal include Mexican Opal, Jelly Opal, Water Opal, and Fire Opal, depending on its appearance and origin.
Claro Opal, like other opals, generally has a hardness of about 5.5 to 6.5 on the Mohs scale, making it relatively soft compared to many other gemstones. This means it is somewhat susceptible to scratching and needs careful handling and maintenance.
The refractive index of Claro Opal typically ranges from about 1.37 to 1.52. This contributes to its famous play-of-color.
Claro Opal exhibits a subvitreous to waxy luster, which is part of what gives it a unique visual appeal.
Opal, including Claro Opal, typically does not exhibit any cleavage, which is a break along crystallographic structural planes.
Claro Opal is characterized by a conchoidal fracture, which can result in smooth, curved surfaces when the stone is broken.
The specific gravity of Claro Opal ranges approximately from 1.98 to 2.25, which is considered relatively low and is indicative of its significant water content.
Claro Opal is an isotropic gemstone, meaning it does not exhibit double refraction when viewed under polarized light.
Opals are well-known for their dispersion or “”fire,”” which refers to the stone’s ability to disperse light into various colors. Claro Opal, with its transparent to translucent nature, can display a brilliant play of color depending on the conditions of formation and specific internal characteristics.
Claro Opal is amorphous, meaning it does not have a crystalline structure. This is typical of opaline substances.
Claro Opal can show a wide range of colors, including clear through various shades depending on impurities and conditions during formation. It is particularly valued for its vivid play of color.
This type of opal ranges from transparent to translucent, which allows for light to pass through and contributes to its color play.
Pleochroism is not typically observed in Claro Opal due to its amorphous nature.
Claro Opals can show fluorescence under ultraviolet light, typically displaying a greenish or white glow, although this can vary.
Opal’s toughness can be considered fair to poor because of its higher water content and relative softness.
Claro Opal is generally brittle, making it susceptible to being damaged under stress.
Being isotropic, Claro Opal does not have an optic sign.
Claro Opal does not have a characteristic absorption spectrum due to its amorphous structure and variability in composition.
Opals, including Claro Opal, are primarily composed of silica (SiO2) and water, with the water content potentially reaching up to 20% by weight.
While not as common as in some other gemstones, some Claro Opals may exhibit a cat’s eye effect if they have aligned fibrous inclusions.
Asterism, or the star effect, is rare in Claro Opals and generally not a feature associated with this type of opal.
One of the most appealing features of Claro Opal is its iridescence, where the stone shows changing colors in different lighting conditions.
Claro Opal is not magnetic.
As a non-metallic mineral, Claro Opal has poor electrical conductivity.
Claro Opal is not radioactive.
