Cat's eye [1], namely "cat's eye", "cat's eye" and "cat essence". Opal, also known as oriental cat's eye, is a rare and precious variety in jewelry. Opal is named because it is as flexible and bright as a cat's eye and can change with the intensity of light. This optical effect is called "cat's eye effect". Cat's eye refers to the emerald with cat's eye effect. Among all gems, there are many kinds of gems with cat's eye effect, but in national standards, only chrysoberyl with cat's eye effect can really be called cat's eye, and other gems with cat's eye effect can't be directly called cat's eye. Gemmologists call the chrysoberyl with cat's eye effect opal. Generally speaking, opal refers to emerald-green cat-eye gemstone, while other gemstones with cat-eye effect must be preceded by the word "cat's eye", such as aquamarine cat's eye and tourmaline cat's eye. This kind of gem has parallel "tubular" inclusions in the crystal, so after being processed into an arc-shaped gem, it can reflect light intensively and appear a cat's eye-like light band. Under the illumination of the spotlight flashlight, the rotating cat's eye jewel will open and close, just like the cat's eye, hence the name "cat's eye".
Source minerals
Opal is a kind of gold emerald in mineralogy and belongs to spinel mineral. Gold emerald is an alumina containing beryllium, and its chemical molecular formula is BeAl2O4. Primary mineral crystals are often tabular and short columnar, belonging to orthogonal crystal system. Crystal morphology is often short columnar or plate-shaped. Opal has many colors, such as honey yellow, brownish yellow, wine yellow, brownish yellow, yellowish green, yellowish brown, grayish green and so on, among which honey yellow is the most precious. Transparent to translucent. The glass is greasy and shiny. The refractive index is 1.745- 1.755, and the birefringence is 0.008-0.0 10. Dichroism is obvious, the dispersion is 0.0 15, and it is not isotropic. The hardness is 8-8.5, and the density is 3.71-3.75g/cm3. Shell fracture. Common colors are gold, yellow-green, gray-green, brown, brown and so on. The cause of color is that emerald minerals contain fluoride ions.
cause
The cause of cat's eye is that there are a lot of fine, dense and parallel filamentous rutile inclusions in chrysoberyl minerals, and the refractive index of rutile is 2.60-2.90. Due to the great difference in refractive index between chrysoberyl and rutile, the incident light is reflected by rutile inclusions and concentrated into light to form a cat's eye. The more opaque the chrysoberyl is, the denser the rutile filamentous inclusions are, and the more obvious the cat's eye effect is. When the jewel in the cat's eye is illuminated by a spotlight flashlight, at a certain angle, the cat's eye appears yellow to half of the light, while the other half appears milky white. If two spotlight flashlights are used to illuminate the cat's eye from two directions, and the gem is rotated back and forth around the direction of the filamentous inclusion, you can see that the cat's eye line opens for a while and closes for a while.
Main producing areas
Mainly produced in Sri Lanka, Brazil and other places, Sri Lanka cat's eye has always been world-renowned.
Identification method
Cat's eye gem is a precious gem, and its quality is mainly determined by color, eyeliner and weight. , briefly introduced as follows:
1. Color: There are many colors of cat's eyes, with yellow as the main color and other shades. The best color is honey yellow, followed by yellow-green, brown-green, brown and brown.
2. Eyeliner: Eyeliner should be straight, even and uninterrupted, clear and not turbid, bright and not gloomy;
3. Weight: For gems, the greater the weight, the more their value increases geometrically. For cat eyes, it is no exception. There are few in the market, especially those with a diameter greater than 5cm.
Stone cat's eye: golden green cat's eye, that is, when the cat's eye contains chromium, sometimes it will show color-changing effect, which is very expensive and rare.
Physical properties of cat's eye
Hardness: 7
Specific gravity: 2.53g/cm3
Cleavage: no cleavage
Fracture: Shell fracture.
Color: cyan, gray or green
Stripe: colorless or white
Transparency: transparency
Gloss: glass luster, fracture grease luster.
Luminescence: friction phosphorescence
Others: α -time is piezoelectric.