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Opalized wood is a rare form of petrified wood where the original organic material has been replaced by opal (hydrated silica) through a mineralization process spanning millions of years. The transformation occurs when silica-rich water infiltrates buried wood, preserving the cellular structure while converting it into precious opal.
This fossilized material exhibits distinctive play-of-color characteristics inherent to precious opal, displaying iridescent flashes of blue, green, and red while maintaining the original wood grain patterns and growth rings. The mineralization process preserves microscopic details of the wood’s cellular structure, including tracheids, vessels, and medullary rays, making it valuable for both paleobotanical research and gemology.
Found predominantly in Australia’s opal fields, particularly in New South Wales and South Australia, opalized wood specimens date primarily from the Cretaceous period, approximately 100-120 million years ago. The finest examples showcase both the spectacular optical properties of precious opal and the intricate botanical features of ancient wood, creating unique specimens prized by collectors and researchers alike.
Opalized wood is typically a natural gemstone.
Common names for Opalized wood include petrified opal wood, opalized petrified wood, and wood fossil opal.
Opalized wood, being a form of petrified wood that has been replaced with opal, typically has a hardness rating of around 5.5 to 6.5 on the Mohs scale. This is due to the silica content from the opal.
The refractive index of opalized wood can vary depending on the type and proportion of opal present. Generally, the RI can range from approximately 1.37 to 1.52.
Opalized wood displays an opalescent luster due to the opal replacement, which can give it a waxy to glossy appearance.
Opal, and consequently opalized wood, does not have a cleavage as opal is an amorphous mineraloid.
The fracture in opalized wood is typically conchoidal or uneven, which is characteristic of opal.
The specific gravity of opalized wood generally ranges from about 1.98 to 2.25, depending on the composition and the type of opal (whether it is common opal or precious opal).
Opalized wood, made up of opal, shows no birefringence as opal is isotropic due to its amorphous nature.
The dispersion or fire of opalized wood can be quite pronounced if the opal content is high and of the variety known as precious opal, which is known for its play of color.
Being composed of opal, opalized wood does not have a crystal system per se, as opal is amorphous.
The color of opalized wood can vary widely, including white, gray, black, various shades of brown, and even vibrant colors if it includes precious opal.
Opalized wood can range from opaque to translucent, depending on the density and type of the opal material that has replaced the original wood structure.
Opalized wood does not display pleochroism due to the isotropic nature of opal.
Some types of opalized wood may fluoresce under UV light, typically showing green or white colors. This depends on the trace elements present in the opal.
The toughness of opalized wood is generally fair to good, although opal can be somewhat brittle and sensitive to cracking.
Opalized wood is generally brittle, as is characteristic of opal.
Opalized wood, being composed of opal, is isotropic and thus shows no optic sign.
Opalized wood typically does not have a distinctive absorption spectrum due to the amorphous structure of opal.
The primary chemical composition of opalized wood is SiO₂·nH₂O; it is primarily silica with varying amounts of water content.
Although not common, some opalized woods can exhibit a cat’s eye effect if the fibrous structure of the wood is preserved and aligned appropriately.
Asterism is not typically observed in opalized wood.
Opalized wood can exhibit iridescence, especially if it includes segments of precious opal, which is known for its spectral play of color.
Opalized wood is not magnetic.
Being mostly composed of opal, opalized wood is generally a poor conductor of electricity.
Opalized wood is not radioactive.
