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Opalized bone is a form of fossilized remains where the original organic material has been replaced by opal through a mineralization process known as permineralization. The process occurs when silica-rich water infiltrates bone tissue, gradually replacing the organic matter while maintaining the original bone structure at a microscopic level.
These rare specimens form under specific geological conditions where dissolved silica in groundwater deposits within the void spaces of decomposing bone tissue. The resulting fossils exhibit both the structural characteristics of bone, including Haversian canals and lacunae, and the optical properties of precious opal, including play-of-color in some specimens. Notable deposits of opalized bone have been discovered in Australia’s Cooper Basin and Lightning Ridge regions, where marine reptile remains from the Cretaceous period have undergone this unique preservation process. The scientific value of opalized bones extends beyond paleontology into the fields of mineralogy and taphonomy, providing insights into ancient environmental conditions and fossilization processes.
Opalized bone is typically a natural gemstone.
Common names for Opalized bone opal include bone opal, opalized fossil, and fossilized opal.
Opalized bone, like other opal types, generally ranges in hardness from 5.5 to 6.5 on the Mohs scale. This makes it relatively softer compared to many other gemstones, and somewhat susceptible to scratching and wear.
Opalized bone typically has a refractive index in the range of 1.44 to 1.46, which is characteristic of opal.
The luster of opalized bone can vary significantly depending on its quality and type, ranging from subvitreous to waxy.
Opal, including opalized bone, does not exhibit cleavage but can be somewhat brittle.
Opalized bone typically exhibits a conchoidal fracture, which is a curved breakage surface similar to that of glass.
The specific gravity of opalized bone usually falls between 1.98 and 2.20, depending on the precise mineral content and porosity.
Opal, including opalized bone, is amorphous and does not exhibit birefringence due to its lack of crystalline structure.
Opalized bone can exhibit a notable play of color or “”fire,”” which is caused by the diffraction of light passing through its silica structure. This characteristic, however, varies greatly among specimens.
Being an amorphous mineraloid, opalized bone does not belong to any crystal system.
The color of opalized bone can vary widely, including white, cream, blue, green, red, and a range of other hues depending on the conditions under which it was formed.
Opalized bone ranges from opaque to translucent, with variations largely dependent on the structure and composition of the original bone and the opal formation.
Opal, including opalized bone, typically does not display pleochroism due to its amorphous nature.
Some opalized bones may exhibit fluorescence under ultraviolet light, typically glowing green or white, depending on the specific mineral impurities present.
The toughness of opalized bone can be considered fair to poor, as opal is generally sensitive to impact and temperature changes.
Opalized bone is generally brittle, with a tenacity that does not tolerate rough handling or high pressure.
As an amorphous material, opalized bone does not have an optic sign.
Opalized bone does not typically show a distinctive absorption spectrum due to its amorphous nature and varied composition.
Opalized bone primarily consists of silica (SiO2·nH2O) with varying amounts of water. The original organic material of the bone is replaced by silica over geological timeframes.
While less common in opalized bone, some specimens may exhibit chatoyancy when cut appropriately, especially if the structure includes aligned fibrous inclusions.
Asterism or a star effect is rare in opalized bone but can occur in some specimens if included crystals are oriented in a specific repetitive pattern.
Opalized bone often displays iridescence, showing different colors when viewed from different angles, due to the diffraction of light through its microstructure.
Opalized bone is generally non-magnetic.
Being composed mostly of silica, opalized bone is an insulator and does not conduct electricity effectively.
Opalized bone is typically not radioactive. However, testing is advisable if there is uncertainty about the presence of radioactive minerals in the surrounding rock or sediment.
