The first requirement for a gem is that it is absolutely beautiful, pure, uniform, transparent and dazzling, or exhibits special optical effects such as cat's eye, starlight, discoloration and discoloration. For example, a colorless, transparent and flawless diamond is the king of gems, and opaque black diamonds are only used for industrial purposes, which is the major difference between beauty and ugliness.

Rare things are precious, and this famous saying can best be reflected in precious stones. The rarer a gem is, the more precious it is. Amethyst, for example, was first discovered in Europe centuries ago, although it is very small. However, because of its bright and novel colors, it is very popular with people. Because of its rarity, it was valued for its eyesight at that time. However, after the discovery of a large amethyst mine with high quality in South America, the price of amethyst plummeted and it no longer enjoys a precious name.

Gems are not only colorful and extraordinary, but also need to have the durability characteristics of always maintaining their beautiful appearance, that is, gems must be hard and wear-resistant and have high chemical stability.

As a qualified gem, at least the following three conditions must be met. Beauty: This is the first condition, which requires bright, pure, transparent and flawless color, bright luster or special optical effects such as color change, color change, light display or cat's eye. Durability: It is required to have the durability to keep gorgeous and shiny, that is, it must be hard, wear-resistant and have good chemical stability. Rare: it means that the output is scarce.