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".