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Light crystal opal is a transparent to translucent variety of precious opal displaying vibrant play-of-color against a clear to white base, characterized by its high clarity and distinct spectral flash patterns. The gemstone exhibits a unique internal structure of uniformly-sized silica spheres arranged in a regular grid-like pattern, creating diffraction of light that produces iridescent color displays.
The optical phenomenon in light crystal opal occurs through Bragg diffraction, where light waves interact with the ordered microstructure of silica spheres, typically ranging from 150 to 300 nanometers in diameter. These spheres contain 3-21% water content within their amorphous silica framework, contributing to the gem’s refractive index of 1.37-1.47. The stone’s distinctive play-of-color manifests in broad flash patterns, displaying pure spectral colors across its surface when viewed from varying angles.
Mining locations for premium light crystal opal include Lightning Ridge in New South Wales, Australia, where specimens form in alkaline conditions within weathered claystone bands, typically at depths of 30 meters below surface level.
Light crystal is typically a natural gemstone.
Common names for Light crystal opal include jelly opal, water opal, and girasol opal.
Crystal opal, like other opals, ranks about 5.5 to 6.5 on the Mohs scale of mineral hardness. This relatively low hardness means it’s more susceptible to scratching and wear than harder gemstones like diamonds or sapphires.
The refractive index of crystal opal typically ranges from 1.37 to 1.52. This is relatively low compared to many other gemstones, contributing to its unique visual properties.
Crystal opal exhibits a vitreous to sub-vitreous luster when cut and polished, giving it a glass-like surface that enhances its play of color.
Opal, including crystal opal, does not have any cleavage. This means it does not break along any specific planes of weakness, which is typical for this amorphous mineraloid.
Crystal opal commonly exhibits a conchoidal fracture, where breaks are curved and shell-like. This is typical of materials with an amorphous structure.
The specific gravity of crystal opal is typically between 1.98 and 2.25. This range can vary slightly depending on the impurities and structure of the specific specimen.
Crystal opal is isotropic and shows no birefringence due to its amorphous nature. Light travels through crystal opal at a consistent speed regardless of the light’s direction.
Crystal opal is particularly noted for its outstanding dispersion of light, often referred to as ‘fire’. This creates a spectacular display of flashing rainbow colors, which can include blues, greens, reds, and oranges.
As an amorphous mineraloid, crystal opal does not have a crystal system. It lacks a long-range, orderly crystalline structure.
The body color of crystal opal can range from transparent to semi-transparent, often displaying a clear or slightly milky background which allows for a vivid play of color.
Crystal opal is known for its transparency or semi-transparency, which distinguishes it from other forms of opal that are often opaque.
Crystal opal does not display pleochroism due to its isotropic nature.
Crystal opal can show fluorescence under ultraviolet light, typically glowing green or white. This property varies depending on the origin and specific conditions of the formation of the opal.
Opal has fair to poor toughness due to its relatively high water content and internal structure, making it more vulnerable to cracking under impact.
Crystal opal is generally brittle, making it prone to chipping or cracking under stress.
Being isotropic, crystal opal has an optic sign of “”none.””
Crystal opal does not typically display a characteristic absorption spectrum due to its amorphous nature and variability in composition.
Crystal opal is primarily composed of silica (SiO2) and water. It can contain up to 20% water by weight, which significantly influences its physical properties.
While less common in crystal opal compared to other gemstones like chrysoberyl, some specimens can exhibit a cat’s eye effect when properly cut.
Asterism or the star effect is not typically observed in crystal opal.
The iridescence, or play of colors, is one of the most defining characteristics of crystal opal. This phenomenon is due to the diffraction of light passing through tiny silica spheres within the structure of the opal.
Crystal opal is not magnetic.
Being a form of silica, crystal opal is generally a poor conductor of electricity.
Crystal opal is not radioactive.
