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Hungarian opal is a precious hydrated amorphous form of silica (SiO2·nH2O) found exclusively in the ancient volcanic regions near Vörösvágás, Hungary. This gemstone exhibits a distinctive play-of-color phenomenon through diffraction of light across regularly arranged microscopic silica spheres within its internal structure.
The stone formed during the Miocene epoch through hydrothermal processes in volcanic host rocks, primarily rhyolite and tuff. Hungarian opals display a unique “”pinfire”” pattern – small, intense points of spectral color against a typically milky-white to translucent base. The material contains 6-10% water content and demonstrates a hardness of 5.5-6.5 on the Mohs scale.
Mining of Hungarian opal peaked during the late 19th century, when the deposits supplied 95% of the world’s precious opal market. The stones gained particular fame in the Habsburg court, with specimens displayed in Vienna’s Natural History Museum and the Hungarian National Museum in Budapest. Modern specimens are exceptionally rare, as most historic mines have been depleted.
Hungarian Opal is typically a natural gemstone.
Common names for Hungarian Opal include Tokay Opal, Hungarian Agate Opal, and Hungarian Fire Opal.
Hungarian opal, like other varieties of opal, typically has a hardness of about 5.5 to 6.5 on the Mohs scale. This makes it relatively softer compared to many other gemstones, which means it can be more susceptible to scratches and abrasions.
The refractive index of Hungarian opal ranges from approximately 1.42 to 1.43, which is relatively low compared to other gemstones. This characteristic affects how much the light bends when entering the stone.
Hungarian opal exhibits a subvitreous to waxy luster, which contributes to its unique visual appeal. The luster can vary slightly depending on the opal’s type and the conditions under which it was formed.
Opals, including Hungarian opal, generally do not have a cleavage because they are amorphous. This means that they do not have a crystalline structure that splits along definite planes.
The fracture of Hungarian opal is typically conchoidal (shell-like), which is common in non-crystalline minerals. This type of fracture can create a smooth surface when the stone is broken.
The specific gravity of Hungarian opal varies slightly, typically ranging from about 2.15 to 2.20. This measurement indicates the density of the gemstone compared to water.
Opal, including Hungarian opal, is isotropic and does not exhibit double refraction. This property means that the gemstone has the same optical properties in all directions.
Hungarian opal can display a play of color or “”fire,”” which is caused by its internal structure diffracting light into various colors. The dispersion is not particularly high in numerical terms but is visually significant due to the play of color.
Hungarian opal is amorphous, meaning it does not have a crystalline structure. Its internal structure consists of silica spheres that are randomly packed.
Hungarian opal can come in a variety of colors, including white, gray, blue, green, and pink. The colors can appear milky or translucent, depending on the type of opal.
The transparency of Hungarian opal can vary from opaque to translucent. Some stones may even approach transparency, depending on their formation and the specific conditions of their environment.
Hungarian opal does not exhibit pleochroism. This property is generally associated with crystalline gems and involves changes in color when viewed from different directions, which does not occur in amorphous minerals like opal.
Some varieties of Hungarian opal may exhibit fluorescence under ultraviolet light. The fluorescence can vary, typically showing white or greenish colors.
Opal is generally considered to have fair to good toughness, but it can be prone to cracking and chipping due to its relatively high water content and lack of crystalline structure.
Hungarian opal is brittle, which is a common characteristic of opals due to their amorphous nature and internal structure.
Being isotropic, Hungarian opal does not have an optic sign as it behaves the same optically in all directions.
Hungarian opal does not typically display a characteristic absorption spectrum due to its amorphous nature and lack of uniform internal structure.
Hungarian opal is primarily composed of silica (SiO2) and water. It can contain up to 10% water by weight.
While not common, some Hungarian opals may exhibit chatoyancy when cut properly, showing a cat’s eye effect if it contains aligned fibers or inclusions.
Asterism, or the star effect, is not typically associated with Hungarian opal due to its amorphous structure and random internal pattern.
The iridescence in Hungarian opal, known as opalescence, is a defining feature. This phenomenon is caused by the diffraction of light by the silica spheres within the opal’s structure.
Hungarian opal is not magnetic due to its chemical composition, lacking magnetic minerals.
As a non-metallic mineral, Hungarian opal is a poor conductor of electricity.
Hungarian opal is not radioactive and poses no known risks of radioactivity.
