The value of opal

The value of opal:

The cat's eye refers to the gold emerald with cat's eye effect. Among all the gemstones, there are many gemstones with cat's eye effect, but only the gold emerald with cat's eye effect can be directly called cat's eye in the national standard. Other gemstones with cat's eye effect are Can not be directly called the cat's eye. The gold emerald mineral is bismuth aluminum oxide (BeAl2O4). The primary mineral crystals are usually plate-like and short-columnar crystals. They are orthorhombic, with a refractive index of 1.745-1.755, a density of 3.76g/cm3 and a hardness of 8-8.5. Common colors are golden yellow, yellowish green, grayish green, brown, brownish yellow, etc., and the color is caused by the inclusion of F ions in the gold emerald mineral. Cat eyes are mainly produced in Sri Lanka, Brazil and other places, Sri Lankan cat eyes have been known for the world.

The reason for the cat's eye is that there are a large number of fine, dense and parallel filamentous rutile mineral inclusions inside the gold emerald mineral. The refractive index of rutile is 2.60-2.90, due to the refractive index of gold emerald and rutile. The larger difference is that the incident light is reflected by the rutile inclusions and concentrated into a light to form a cat's eye. When the gold emerald is more opaque and the rutile filamentous inclusion is denser, the cat's eye effect is more obvious. When a cat litem is illuminated with a spotlight, at one angle, the cat's eye appears yellow to half of the light, while the other half appears milky white. If two concentrating flashlights are used to illuminate the cat's eye from both directions, and at the same time, the gemstone is rotated back and forth with the direction of the filamentous enveloping body as an axis, the cat's eyeliner is opened for a while and closed for a while.

Cat's eye gemstone is a kind of precious gemstone. Its quality is mainly determined by color, eyeliner, weight, etc., and is briefly described below:

1, color: cat color has a variety of colors, mainly with other shades of yellow, the best color is honey yellow 60,000 yuan, the other is yellow green, brown green is more than 70,000, brown yellow is the most expensive each Above 90,000 yuan, brown price is 30,000 yuan;

2, eyeliner: eyeliner requires straight, uniform, continuous and continuous line, clear and not turbid, bright and not dark;

3, weight: For gemstones, the greater the weight, the value of geometric increase, for the cat's eye, is no exception, the market has been very few, and the diameter is greater than 5cm is less common.