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Gold opal is a precious gemstone variety characterized by a dominant yellow to golden background color with vibrant play-of-color flash patterns across its surface. The stone forms when silica spheres arrange in a regular pattern within hydrated silica dioxide, creating a three-dimensional diffraction grating that splits white light into spectral colors.
Found primarily in Australia’s Lightning Ridge and Coober Pedy regions, gold opal exhibits a base color caused by iron oxide inclusions within its microstructure. The gem’s internal architecture consists of uniformly sized and stacked silica spheres approximately 150-300 nanometers in diameter, producing iridescent optical phenomena through Bragg diffraction. These spheres create a photonic crystal structure that displays characteristic golden undertones with rainbow-like flashes.
The stone ranks 5.5-6.5 on Mohs hardness scale and possesses a specific gravity between 2.0-2.2. Its unique optical properties stem from both constructive and destructive interference of light waves within its microscopic structure, resulting in the distinctive golden body color combined with dynamic spectral displays.
Gold Opal is typically a natural gemstone.
Common names for Gold Opal include Golden Opal, Sun Opal, and Yellow Opal.
Gold opal typically has a hardness of 5.5 to 6.5 on the Mohs scale, which means it is relatively soft and needs careful handling to prevent scratching.
The refractive index of gold opal ranges from approximately 1.44 to 1.46, which contributes to its distinctive play of color.
Gold opal exhibits a subvitreous to waxy luster, which makes it less shiny compared to gems like diamonds but contributes to its unique visual appeal.
Opal, including gold opal, generally does not display cleavage. This is a property where a mineral tends to break along specific planes.
Gold opal typically exhibits a conchoidal fracture, which results in a smooth, curved surface when the stone is broken.
The specific gravity of gold opal ranges from about 1.98 to 2.25, which is relatively low compared to many other gemstones.
Opal, including gold opal, is an amorphous mineraloid and does not have a crystalline structure, thus it does not exhibit birefringence.
Gold opal can display a remarkable play of color or “”fire,”” which is caused by the diffraction of light through its silica sphere structure. The exact level of dispersion can vary depending on the quality of the opal.
Gold opal is amorphous, meaning it does not have a regular crystal structure. This is typical of all types of opal.
Gold opal displays a vibrant mix of colors with a predominant golden hue that can range from yellow to deep orange, often accompanied by flashes of green, blue, and red depending on the angles of light.
Opals, including gold opal, can range from opaque to translucent. The degree of transparency affects the stone’s appearance and value.
Gold opal does not display pleochroism due to its amorphous nature.
Some opals may fluoresce under ultraviolet light, typically showing a white or greenish glow. The fluorescence of gold opal can vary.
Opal is generally considered to have fair to good toughness, but it can be prone to cracking or “”crazing”” due to its water content and internal structure.
Gold opal has a brittle tenacity, which means it can break or chip relatively easily compared to more tenacious minerals.
Being amorphous, gold opal does not have an optic sign. This property is relevant only to crystalline materials.
Typically, opals do not have a well-defined absorption spectrum due to their amorphous nature and unique internal structure.
Gold opal is primarily composed of silicon dioxide (SiO2) and water (H2O). The water content can range from 3% to 21% by weight.
While not common in all opals, some gold opals may exhibit chatoyancy or a “”cat‚Äôs eye”” effect when cut into a cabochon with the appropriate orientation.
Asterism or the star effect is rare in opals, including gold opal. This effect is more typically found in sapphire or ruby.
One of gold opal’s most prized features is its iridescence, which displays a moving rainbow of colors that change with the angle of light.
Gold opal is non-magnetic, which is typical for silicate minerals.
Being composed mostly of silica, gold opal has low electrical conductivity.
Gold opal does not exhibit radioactivity, making it safe for various applications including jewelry and decorative items.
