Opal (cat. Seye), namely "golden emerald with cat's eye effect", "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. Because the light phenomenon of opal is as flexible and bright as cat's eye, it can change with the intensity of light, so it is named.

The value of golden green cat's eye is mainly influenced by color, eyeliner effect, size and thickness. The highest value is the real cat's eye of beeswax yellow, the light yellow and green are slightly worse, and the worst is grayish white. A good golden green cat's eye requires the eyeliner to be located in the middle of the arc, clear and bright, and flexible to open and close. The golden green cat's eye is a precious gem, rarely exceeding 2 carats, so its size has a great influence on the price. Among the gems of the same size, the price of a gem with a thick waist is obviously lower than that of a gem with a moderate waist. This is because the bent gem is too thick, which not only increases the weight but also is not conducive to inlay. Defects and cracks will seriously affect and reduce the value of gems. Generally speaking, the more obvious the discoloration effect, such as emerald green during the day and bright red at night, the higher the price. But in general, there are few gems with such obvious discoloration effect. Generally, it is dark green during the day and reddish brown at night, that is, it is like green tourmaline during the day and pomegranate red at night. In the size of metamorphic rocks, large metamorphic rocks are less, so the price is more expensive. Generally speaking, metamorphic rocks with large particles, high transparency and few defects have higher prices. The international price of high-quality variable stone can reach $0/000-5000 per carat/kloc. Generally speaking, the evaluation of emeralds is often based on color beauty, particle size, number of defects and other factors. Opal is very precious because of its special light effect. High-quality opal over 10 carat can be worth millions of dollars.