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Red flash opal is a rare variety of precious opal exhibiting a distinct red-orange flash or play-of-color phenomenon when viewed from specific angles under direct light. This phenomenal gemstone belongs to the mineraloid class of hydrated amorphous silica (SiO2·nH2O), featuring a unique internal structure of uniformly sized silica spheres arranged in a regular pattern.
The distinctive red flash effect results from the diffraction of light through the opal’s microscopic silica sphere grid structure, which typically measures between 150 to 300 nanometers in diameter. These opals form in silica-rich environments through the slow deposition of colloidal silica gel in rock fissures and cavities. Most high-quality red flash opals originate from Australia’s Lightning Ridge region, where they develop within ironstone concretions under specific geological conditions involving alkaline groundwater and weathered sandstone deposits.
Red flash opal is typically a natural gemstone.
Common names for Red Flash Opal include Cherry Opal, Fire Opal, and Scarlet Opal, among others.
Red flash opal typically has a hardness of 5.5 to 6.5 on the Mohs scale, making it relatively softer compared to many other gemstones. This lower hardness level means that red flash opal is more susceptible to scratches and abrasion, thus requiring careful handling and storage.
The refractive index of red flash opal ranges from about 1.37 to 1.52. This indicates how much the gemstone bends light, a factor that contributes significantly to its famed play of color.
Red flash opal has a subvitreous to waxy luster, giving it a beautiful sheen that enhances its visual appeal.
Opal, including red flash opal, typically does not display any cleavage, which is a measure of how a mineral breaks along its crystallographic planes. The absence of cleavage makes opal more fragile and prone to chipping.
This gemstone usually exhibits a conchoidal fracture, which is characterized by smooth, curved surfaces and is typical of more brittle materials.
Red flash opal has a specific gravity typically ranging between 1.98 and 2.25, which can vary depending on the type and structure of the opal.
Opal, including red flash opal, is an isotropic gemstone, meaning it has no double refraction. Light passes through the gemstone uniformly regardless of the light’s angle of entry.
Red flash opal is renowned for its dispersion or fire, which manifests as a play of spectral colors. This property is especially visible when the stone is turned under a light source.
Red flash opal crystallizes in the amorphous system, lacking a defined crystalline structure due to its formation from silica gel.
Red flash opal displays a primary body color from transparent to white, with vibrant flashes of red and potentially other colors, depending on the angle of light.
This gemstone ranges from transparent to opaque. The level of transparency significantly affects the value and appearance of the opal.
Red flash opal does not exhibit pleochroism due to its isotropic nature, meaning the color remains constant regardless of the viewing angle.
Some opals may exhibit fluorescence under ultraviolet light, typically showing a white to cream or greenish glow. However, the presence and strength of fluorescence can vary.
Despite its beauty, red flash opal is relatively fragile and has poor toughness, making it prone to cracking and breaking, particularly in response to sudden temperature changes or impacts.
The tenacity of red flash opal is generally considered to be brittle, which is a common trait among opals due to their internal structure and water content.
Being isotropic, red flash opal does not have an optic sign as it behaves the same optically in all directions.
Typically, red flash opal does not have a characteristic absorption spectrum. Instead, its color play is due to the diffraction of light by silica spheres within its structure.
Red flash opal is primarily hydrous silicon dioxide (SiO2·nH2O), with its water content varying but typically being between 3% and 10%.
This effect is rarely seen in red flash opals as it requires aligned fibrous inclusions, which are not common in this type of opal.
Like chatoyancy, asterism or the star effect is not typically observed in red flash opals due to the lack of necessary crystal inclusions.
The iridescence or color play in red flash opal is one of its defining features, resulting from the diffraction of light by microscopic layers of silica spheres within the stone.
Red flash opal exhibits no magnetic properties due to its chemical composition and lack of metallic elements.
Being composed largely of silica, red flash opal is a poor conductor of electricity.
Red flash opal is not radioactive and poses no health hazards in this regard.
This detailed profile of red flash opal highlights its unique physical and optical properties, which contribute to its desirability as a gemstone but also necessitate careful handling and maintenance.
