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Bone opal is a rare fossilized material formed when ancient animal bones undergo mineralization, where the original organic matter is replaced by opal through silicification processes. This unique gemstone preserves the microscopic structure of the original bone tissue while displaying the characteristic play-of-color associated with precious opal.
The formation occurs in sedimentary deposits where silica-rich groundwater penetrates fossilized bone material, gradually replacing the calcium phosphate of the bone with hydrated silica. The resulting material exhibits distinctive Haversian canals and osteocytes visible under microscopic examination, combined with the iridescent optical phenomena created by the regular arrangement of silica spheres. These specimens predominantly originate from Lightning Ridge, Australia, where they form in Cretaceous period deposits approximately 110 million years old. The most valuable specimens display vivid color play against a dark body tone, often featuring red, blue, and green flashes across the preserved bone structure.
Bone Opal opal is typically a natural gemstone.
Common names for Bone Opal include Dendritic Opal, Merlinite, and Moss Opal.
Bone opal typically falls between 5.5 to 6.5 on the Mohs scale, similar to that of most opals, indicating a relatively soft gemstone that needs careful handling to avoid scratching.
The refractive index of bone opal generally ranges from about 1.42 to 1.45, which is similar to other types of opal.
Bone opal exhibits a subvitreous to waxy luster, which contributes to its unique and appealing visual properties.
Like other opals, bone opal does not have a true cleavage but may exhibit a conchoidal fracture, which is characteristic of many amorphous or cryptocrystalline minerals.
Bone opal typically displays a conchoidal fracture, which is a curved fracture surface commonly seen in glass and other amorphous substances.
The specific gravity of bone opal usually lies between 1.98 and 2.25, which is slightly denser than some other varieties of opal.
As an amorphous gemstone, bone opal does not exhibit double refraction, maintaining a uniform refraction of light throughout the stone.
Bone opal can display a range of color play or fire, though typically less brilliant than that seen in precious opals. The fire depends on the conditions in which the opal formed and the size and arrangement of its silica spheres.
Being amorphous, bone opal does not belong to any crystal system. It is made up of silica spheres that are randomly packed, lacking a long-range crystalline order.
Bone opal can vary in color but often exhibits white to cream or beige hues, potentially mixed with other color patches or play-of-color depending on the variety and location of the material.
The transparency of bone opal can range from opaque to slightly translucent depending on the structure and thickness of the opal.
Pleochroism is absent in bone opal due to its amorphous nature. The color seen is usually consistent regardless of the angle of viewing.
Bone opal may show weak to moderate fluorescence under UV light, often displaying green, white, or no fluorescence at all, depending on its composition and origin.
Due to its relatively high water content and amorphous structure, bone opal has fair to good toughness, making it somewhat resistant to breaking compared to other more brittle gemstones.
Bone opal is generally brittle, like most opals, and can be susceptible to cracking, especially when exposed to sudden changes in temperature or dehydration.
As an isotropic material, bone opal shows a single refractive index and does not exhibit an optic sign.
Bone opal does not typically show a characteristic absorption spectrum due to its amorphous nature and lack of uniform internal structure.
Bone opal is primarily composed of hydrated silica (SiO2·nH2O). The water content can vary significantly, typically between 3% and 10%.
Chatoyancy in bone opal is uncommon but can occur if the stone includes aligned fibrous inclusions.
Asterism, or the star effect, is not generally observed in bone opal due to the lack of aligned needle-like inclusions required to produce this phenomenon.
Some bone opals can display iridescence, characterized by an attractive play of lustrous rainbow-like colors, similar to what is seen in some shells and pearls.
Bone opal exhibits no magnetic properties due to its silica composition.
Being primarily composed of silica, a poor conductor, bone opal exhibits very low to no electrical conductivity.
Bone opal is not radioactive and poses no health hazards related to radioactivity.
