Your Purchases
Rainbow opal is a rare form of precious opal exhibiting a full spectral display of iridescent colors through its internal structure of uniformly-sized silica spheres. This hydrated amorphous form of silica (SiO2·nH2O) diffracts white light into its spectral components through a three-dimensional array of microspheres.
The stone’s distinctive play-of-color occurs through Bragg diffraction within its microstructure, where silica spheres ranging from 150 to 300 nanometers in diameter create a natural photonic crystal. These spheres form a cubic close-packed lattice, producing the characteristic rainbow-like display across the visible spectrum from red (620-750 nm) to violet (380-450 nm).
Found predominantly in Australia’s Lightning Ridge and Ethiopia’s Welo deposits, rainbow opals contain 6-10% water content by weight. Their formation requires specific geological conditions: silica-rich water solutions penetrating into rock cavities under precise temperature and pressure conditions, followed by a slow evaporation process allowing optimal sphere arrangement.
Rainbow opal is typically a natural gemstone.
Common names for Rainbow Opal include Fire Opal, Girasol Opal, and Harlequin Opal.
Rainbow Opal typically has a hardness of 5.5 to 6.5 on the Mohs scale, making it relatively soft compared to many other gemstones. This softness can make it susceptible to scratches and abrasion, so it should be worn and stored carefully.
The refractive index of Rainbow Opal ranges from approximately 1.37 to 1.52, which contributes to its unique play of color and visual properties.
Rainbow Opal exhibits a vitreous to waxy luster, enhancing its appeal and the vibrancy of its play of colors.
Opal, including Rainbow Opal, generally does not exhibit cleavage, which is the tendency of a mineral to break along flat planar surfaces.
This gemstone usually has a sub-conchoidal to uneven fracture, which can make it somewhat brittle and delicate in handling.
Rainbow Opal has a specific gravity typically ranging from about 1.98 to 2.25, varying slightly depending on the amount and type of inclusions and its water content.
Opal is isotropic and shows no double refraction. It is amorphous, meaning it does not have a crystalline structure that causes birefringence.
Rainbow Opal is well-known for its spectacular play of color or “”fire,”” which is caused by the diffraction of light passing through tiny silica spheres within the structure of the opal.
Opal is amorphous, meaning it does not have a regular crystal lattice and does not belong to any crystal system.
Rainbow Opal displays a full spectrum of colors, including blues, greens, reds, oranges, and yellows, often in vibrant and shifting patterns.
This gem can range from opaque to translucent. The degree of transparency can affect the play of color and the stone’s overall visual appeal.
Opal, including Rainbow Opal, does not exhibit pleochroism due to its amorphous nature.
Rainbow Opal can exhibit fluorescence, typically showing a white or light blue glow under ultraviolet light. The presence and strength of fluorescence can vary.
Opal is generally considered to have fair to poor toughness due to its brittleness and high water content, which can make it prone to cracking and chipping.
Rainbow Opal is brittle, which makes it more susceptible to damage during cutting, setting, or wearing.
As an isotropic gem, Rainbow Opal has an optic sign of “”isotropic,”” meaning it has the same optical properties in all directions.
Generally, opals may not show a distinctive absorption spectrum due to their amorphous nature. However, specific impurities or trace elements can sometimes cause faint lines.
Rainbow Opal is primarily made of silica (SiO2) and water. The water content can range from 3% to 21% by weight.
Although less common, some opals like the Rainbow Opal can exhibit chatoyancy when cut properly, which is seen as a single sharp band of light across the surface.
Rainbow Opal does not typically display asterism. This effect is more common in other gemstones with a crystalline structure and suitable inclusions.
One of the most cherished features of Rainbow Opal is its iridescence. This optical phenomenon creates vibrant and changing color patterns, which are best viewed under light movement.
Rainbow Opal is generally non-magnetic, consistent with its composition primarily of silica.
Being composed mostly of silica, Rainbow Opal is a poor conductor of electricity.
Rainbow Opal is not radioactive and is safe for handling and wearing under normal circumstances.
