赖世雄高级美国英语 lesson 17（在线收听）

　　Lesson 17， Precious and Semi-precious Stones 宝石和半宝石

　　"My！ What a beautiful ring you're wearing！" This compliment never fails to flatter and honor the lucky wearer of the ring or other pieces of fewelry bedcked with precious or semi-precious stones. Most people know the names of only some of these natural treasures. Many people are surprised to learn that all semi-precious stones can be bought inexpensively， not to mention that the precious stones can also be had for far less than one imagined. However， as with everything else in life， you have to pay for the best quality. This lesson will give the reader both information and tips on gem stones and their purchase.

　　Just what are precious and semi-precious stones？ The word semi refers to anything which is half or only partial； this， semi-precious stones are not precious， by definition. Actually， some high-quality semi-precious stones are far more expensive than some low-grade precious stones， so the terms "precious" and "semi-precious" when applied to stones do not refer necessarily to their cost.

　　All authorities on gems agree that the diamond， ruby， sapphire， and emerald are precious stones. Some of these experts include the opal as a fifth precious stone while others consider the pearl in this class. The latter may surprise the reader， but on reflection， pearl are also a kind of stone， though organically produced by certain shellfish rather than by geologic forces.

　　Semi-precious stones include all other stones considered worthy of use in jewelry. The list of these stones is very long； suffice it to say that there are several hundred such stones， though most people are aware of only a couple of dozen of their names， and few people can readily recognize more than a couple of any type of stone at all.

　　Diamonds and the colored stones ruby， sapphire， and emerald are often considered the most expensive among all stones. This is generally true， though qualityis more important than stone type on price. One can buy a "real sapphire" for US $10， but it would be considered not much better than junk to a feweler. These professionals consider several features of stones before assessing their value. Carat size， or the weight of the stone （one carat= 200 miligrams） is one such feature. The cut of the stone is another. Some styles of cuts are considered more costly than others； besides， in the technical cutting of the gem form the rough stone， great care must be taken not to cut into or scratch the surface of the finished stone. The color is also important. Rubies， sapphires， and emeralds， for instance， in order to fetch the highest prices， must be solid colored throughout. Finally， clarity or translucence， with neither streaking nor a "cloudy" inner appearance， also determines the final price. Gems with these qualities are far and few between， commanding nearly astronomical prices. A good fewleler will advise you of these characteristics and how to look for and evaluate them yourself. Also remember that for a gem ring or pendant， roughly 70% of the value of the piece of jewelry is in the primary stone（s）， with the rest in labor and metal.

　　Specific names of semi-precious stones are too numerous to mention， but jade is well known to Chinese. The finest jade （apple agree in color） commands very high bids at auction. The trouble with semi-precious stones is that they are not so hard as precious stones so they far more easily scratch， crack， or chip. If this happens， the value of the semi-precious stones plummets. Diamonds， the hardest natural stone， and rubies and sapphires， the second hardest， are actually rather hard to deface.

　　Don't let anyone well you a "good deal on a gem" on the street. Go to several professional jewelers before committing yourself——and your money ——to a piece of jewelry with precious or semi-precious stones. Part of the value of that good piece of fewelry is the fact that it can be handed down generation after generation with increasing value. People in all cultures never seem to tire of the brilliance of gems.