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Cat’s eye opal is a rare variety of opal exhibiting chatoyancy, a distinct optical phenomenon that creates a luminous band of light across its surface, similar to the vertical pupil of a feline eye. This silica-based gemstone forms in metamorphic and sedimentary rocks, containing parallel inclusions of rutile or other minerals that produce the cat’s eye effect when cut en cabochon.
The phenomenon occurs due to the precise alignment of tubular channels within the opal’s microstructure, combined with the play-of-color characteristic of precious opal. These channels, filled with different materials, create a concentrated beam of reflected light perpendicular to their orientation. The most valuable specimens display sharp, well-defined bands against vivid background colors, with specimens from Australia and Brazil commanding premium market prices.
The gemstone measures 5.5-6.5 on the Mohs hardness scale and exhibits a distinctive internal structure that differentiates it from other chatoyant gems like cat’s eye chrysoberyl or quartz. Its unique optical properties make it particularly sought after in both jewelry design and mineralogical collections.
Cat’s eye opal is typically a natural gemstone, though synthetic versions do exist. The natural versions of this gemstone are more valued and sought after.
Cat’s eye opal is also commonly referred to as cymophane when it exhibits notable chatoyancy.
The hardness of cat’s eye opal is typically around 5.5 to 6.5 on the Mohs scale, making it relatively soft and somewhat susceptible to scratches.
The Refractive Index of cat’s eye opal ranges from approximately 1.44 to 1.47.
This type of opal typically has a waxy to resinous luster, which enhances its cat’s eye effect.
Cat’s eye opal has no cleavage, which is a common characteristic of opal in general.
The fracture of cat’s eye opal is typically conchoidal, which is a smooth breakage pattern similar to that of glass.
The specific gravity of cat’s eye opal typically ranges from about 2.15 to 2.23.
Opals, including cat’s eye opal, are isotropic and do not exhibit double refraction.
Cat’s eye opal has low to moderate dispersion, giving it a subtle play of color or “fire” that is highly prized.
Opal is amorphous, meaning it does not have a crystalline structure.
The body color of cat’s eye opal can vary widely, including white, gray, green, brown, and pink.
Cat’s eye opal ranges from opaque to translucent, which affects the visibility of the cat’s eye effect.
Being isotropic, cat’s eye opal does not exhibit pleochroism.
Cat’s eye opal may exhibit fluorescence under UV light, typically showing green or white colors.
Opal is generally considered to have fair to good toughness, but it can be brittle and sensitive to changes in temperature and humidity.
Cat’s eye opal is brittle, which is typical for opal.
Being isotropic, the optic sign of cat’s eye opal is not applicable.
Cat’s eye opal does not have a characteristic absorption spectrum.
Opal is a hydrated form of silica (SiO2·nH2O).
The chatoyancy, or cat’s eye effect, in cat’s eye opal is caused by the reflection of light by parallel fibers, needles, or channels within the stone.
Cat’s eye opal does not typically display asterism.
This type of opal can display iridescence, especially if it has inclusions that diffract light.
Cat’s eye opal is not magnetic.
As a type of opal, cat’s eye opal is an insulator and does not conduct electricity effectively.
Cat’s eye opal is not radioactive.
