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Peruvian opal is a mineraloid hydrated silica (SiO2·nH2O) formed in the Andes Mountains of Peru, distinguished by its semi-opaque to translucent blue-green coloration and unique dendrite inclusions. This volcanic-originated gemstone exhibits a hardness of 5.5-6.5 on the Mohs scale and possesses a vitreous to resinous luster.
The stone forms in volcanic host rocks through low-temperature hydrothermal processes, where silica-rich solutions fill cavities and fractures. Unlike precious opal, Peruvian opal lacks play-of-color but contains trace elements of copper and palygorskite clay minerals, contributing to its characteristic blue-green hue. The material often displays dark, branching manganese oxide dendrites, creating distinctive landscape-like patterns within the stone’s structure.
Mining occurs primarily in the Cajamarca region of northern Peru, where deposits formed during the Miocene epoch approximately 23-5.3 million years ago. The stone’s composition includes 3-9% water content, contributing to its unique optical and physical properties.
Peruvian opal is typically a natural gemstone.
Common names for Peruvian opal include Andean opal, Peruvian blue opal, and Peruvian pink opal.
Peruvian opal has a hardness rating of approximately 5.5 to 6.5 on the Mohs scale, which makes it relatively soft compared to more commonly known gemstones like diamonds or sapphires.
The refractive index of Peruvian opal typically ranges from 1.42 to 1.45, which is relatively low and contributes to its subtle visual effects compared to other more brilliant gemstones.
This gemstone exhibits a waxy to vitreous luster, giving it a soft and appealing glow that is quite distinct from the sparkle of harder stones.
Peruvian opal does not have defined cleavage, which makes it somewhat more durable against breaking along cleavage planes when being cut or polished.
It usually has an uneven to conchoidal fracture, contributing to its unique and natural appearance when cut and polished.
The specific gravity of Peruvian opal ranges from about 2.10 to 2.20, which is typical for opals and indicates a relatively lower density compared to many other gemstones.
Peruvian opal is an amorphous gemstone, lacking a crystalline structure, thus it does not exhibit double refraction.
The dispersion or fire of Peruvian opal is generally low. It does not display the significant play of color seen in precious opals but may show a subtle color play in high-quality specimens.
As an opal, Peruvian opal is amorphous and does not have a crystal system.
Peruvian opal comes in a range of colors, most commonly in shades of blue and green. Less commonly, it can be found in pink. Its colors are typically soft and pastel.
This type of opal ranges from translucent to opaque, which impacts its visual depth and appeal.
Pleochroism is not observed in Peruvian opal due to its amorphous nature.
Peruvian opal generally does not show fluorescence under UV light.
Peruvian opal has fair to good toughness, making it reasonably suitable for jewelry that does not receive rough wear.
The tenacity of Peruvian opal is generally brittle, which is a common characteristic of opal varieties.
Being amorphous, Peruvian opal is isotropic and shows no optic sign.
Peruvian opal does not typically display a distinctive absorption spectrum.
Peruvian opal is a form of hydrated silica (SiO2·nH2O). Its water content may range from 3% to 20%.
While rare, some forms of Peruvian opal can exhibit chatoyancy, especially if cut en cabochon and when fibrous inclusions are present.
Asterism or the star effect is generally not observed in Peruvian opal.
Iridescence is typically not a feature of Peruvian opal, unlike the play of color seen in precious opals.
Peruvian opal is not magnetic.
Being a type of silica, Peruvian opal has poor electrical conductivity.
Peruvian opal is not radioactive.
