Opal is a hydrated amorphous form of silica. Its water content may range from 3 to 21% by weight. But is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid. Unlike crystalline forms of silica, they are classed as minerals. It is deposited at a relatively low temperature.
And it may occurs in the fissures of almost any kind of rock. Being most commonly found with limonite, also sandstone, rhyolite, marl, and basalt.
Depending on the conditions in which it formed, opal may be transparent, also translucent or opaque. And the background color may be white, also black or nearly any color of the visual spectrum. Black opal is considered to be the rarest. Whereas white, also gray and green are the most common.
Cat’s eye opal meaning
In gemology, chatoyancy, chatoyance or cat’s eye effect, is an optical reflectance effect seen in certain gemstones. Coined from the French “oeil de chat”, meaning “cat’s eye”, chatoyancy arises either from the fibrous structure of a material, as in cat’s eye tourmaline, or from fibrous inclusions or cavities within the stone, as in cat’s eye chrysoberyl.
The precipitates that cause chatoyance in chrysoberyl are the mineral rutile, composed mostly of titanium dioxide. Examined samples have yielded no evidence of tubes or fibers. The needles precipitates all align perpendicularly with respect to cat’s eye effect. The lattice parameter of the needles matches only one of the three orthorhombic crystal axes of the chrysoberyl, as a result of an alignment along that direction.
The phenomenon resembles the brilliance of a silk spool. The luminous streak of reflected light is always perpendicular to the direction of the fibers. For a gemstone to show this effect best it must be cut as cabochon, rounded with a flat base rather than faceted, with the fibers or fibrous structures parallel to the base of the finished gem.
Cat’s eye opal
The best finished specimens show a single sharply defined band of light that moves across the stone when it is rotated. Chatoyant stones of lesser quality display a banded effect as is typical with cat’s-eye varieties of quartz. Faceted stones do not show the effect well.
What is cat’s eye opal blue?
Cat’s eye opal blue is a fake stone usually made of synthetic quartz used as healing Feng shui Ball, magical ball or as ornamental stone.
Natural opal for sale in our gem shop
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