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Hyacinth opal is a rare variety of fire opal exhibiting a distinctive reddish-orange to deep red color reminiscent of the hyacinth flower, composed of hydrated silica with microscopic spheres that create its unique play of color. The gemstone forms in volcanic regions where silica-rich solutions penetrate rock cavities, crystallizing under specific temperature and pressure conditions.
The stone’s defining characteristics include its translucent to transparent quality, vitreous luster, and refractive index ranging from 1.43 to 1.46. Its chemical composition of SiO2¬∑nH2O contains trace elements of iron and aluminum oxides, which contribute to its intense coloration. Unlike common opals, hyacinth opals display a more uniform color distribution and higher durability, measuring 5.5 to 6.5 on the Mohs scale.
Primary deposits occur in Mexico’s volcanic regions, particularly in the state of Jalisco, with smaller quantities found in Brazil and Australia. The gem’s formation requires specific geological conditions, including the presence of rhyolitic host rocks and hydrothermal activity, making natural specimens particularly valuable in the gemological market.
Hyacinth Opal is typically a natural gemstone.
Common names for Hyacinth Opal include Fire Opal, Girasol Opal, and Sun Opal.
Hyacinth Opal typically exhibits a hardness of around 5.5 to 6.5 on the Mohs scale, making it relatively softer compared to many other gemstones. This characteristic affects its durability and suitability for different types of jewelry.
The refractive index of Hyacinth Opal generally ranges from approximately 1.44 to 1.46, which is relatively low and contributes to its subtle optical effects compared to more brilliant gemstones.
Hyacinth Opal is known for its vitreous to sub-vitreous luster, giving it a glass-like appearance that is less reflective than gemstones with higher refractive indices.
This gemstone typically does not exhibit cleavage, which is a plane of weakness in its crystal structure. This attribute makes it more resistant to breakage along defined paths.
Hyacinth Opal usually displays a conchoidal fracture, which results in smooth, curved surfaces that are typical of vitreous materials.
The specific gravity of Hyacinth Opal lies in the range of approximately 2.1 to 2.2, which is relatively light, indicating that the gemstone is less dense compared to others.
Hyacinth Opal does not exhibit double refraction, as it is an isotropic material. This means that light passes through the gemstone uniformly, regardless of its direction.
The dispersion or “”fire”” of Hyacinth Opal is generally low, which means it shows less color play or spectral colors when exposed to light compared to high-dispersion gemstones like diamonds.
Hyacinth Opal crystallizes in the amorphous crystal system, lacking a regular crystalline structure, which contributes to its unique visual properties and gemological characteristics.
This gemstone typically presents a hyacinth (orange to red) color, often with a play of color due to the diffraction of light through its silica structure.
Hyacinth Opal ranges from semi-transparent to opaque, which affects its appearance and the way it interacts with light.
Being isotropic, Hyacinth Opal does not display pleochroism — it shows the same color in all directions.
Hyacinth Opal can exhibit weak to moderate fluorescence under ultraviolet light, typically showing green or white colors.
The toughness of Hyacinth Opal is generally fair, but it can be prone to cracking or chipping due to its lower hardness and amorphous nature.
Hyacinth Opal is brittle, making it more susceptible to damage from impact or pressure compared to more tenacious gemstones.
As an isotropic gemstone, the optic sign of Hyacinth Opal is not applicable.
The absorption spectrum of Hyacinth Opal can show broad bands, which are not very distinct due to the gemstone’s general lack of color-causing elements.
Hyacinth Opal consists primarily of hydrated silica (SiO2·nH2O), with its water content varying between 3% and 21%.
While rare in Hyacinth Opal, chatoyancy can occur if the stone contains parallel inclusions or fibrous structures, creating a visible cat’s eye effect when cut en cabochon.
Asterism or the star effect is not typically observed in Hyacinth Opal due to its amorphous structure and lack of aligned inclusions.
Hyacinth Opal may display iridescence, particularly if it contains layers or inclusions that diffract light, creating a rainbow-like effect.
This gemstone is generally non-magnetic.
Hyacinth Opal has low electrical conductivity due to its composition and amorphous nature.
Hyacinth Opal is not radioactive and poses no health hazards in this regard.
