The reason is that things will be easy to get cheap

Precious stones, must have the following characteristics: Cat's Eye
"United States", that is gorgeous crystal, dazzling. If not beautiful gem can not be precious stones, such as the United States or brilliant color performance, or performance of a transparent and clean, or with a special optical effects (such as cat's eye, change color, luminous phenomena), or a special pattern ( such as chrysanthemum stone, agate, jade plum, etc.). For example, the same as the diamond, who used to clear flaw less refined into precious diamonds, and poor transparency, and more flaws, those who color black can only be used as industrial raw materials. "Long", that is, hard wear-resistant texture to enduring. Because the high value of precious stones, people would expect it to durable goods can be preserved or even hereditary. Diamonds have become the most expensive gem, one of the reasons is that it is the world's most hard, and not afraid of corrosion of precious stones, gems and therefore a higher value than the world for a number of hardness, corrosion resistance of silicate minerals (such as Jade) few oxides (such as ruby, sapphire) and elemental minerals (such as diamonds), and soft, susceptible to corrosion of precious stones (such as Jade, Jade South, etc.) lower value in itself, commonly used in the production of handicrafts, in order to work to win; But there are a few gems not included, such as opal, pearl. "Thin", that is, low production. Suddenly, the world is extremely rare emerald, fine quality are per carat (0.2 grams) worth thousands of dollars, and some quite beautiful and can be resistant to "long" gems (such as amethyst), due to production more, extraction easier, the price has been low. Some common rocks, after pondering upon the characteristics of a beautiful and durable, but can not become a member of family gem, the reason is that things will be easy to get cheap.
Arc-type
Arc type: also known as Su-convex type or body type, the viewing surface of a convex. According to kidney-shaped (the shape of the waist), can be further divided into round, olive, heart-shaped, rectangular, square, cross, cushion-shaped, pituitary shape and so on. If the cross-section according to their type, they can be divided into single convex cut, double-convex shape of cut, lentils convex cut, cut hollow convex and concave shape of cut-type five.
Carved face
Carved face: completely covered by a series of geometric planes gemstone surface composition, in accordance with its right angle polishing, gemstone can display in color, brightness, fire and sparkle of four kinds of optical effects. Facet-based and can be divided into diamond-style cut, step-cut, rose-style cut, shear type (cross)-type cut-type and mixed type cut type.