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新东方背诵文选 Lesson 38:Topaz

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Topaz

Topaz is a hard, transparent mineral. It is a compound of aluminum, silica, and fluorine. Gem topaz is valuable. Jewelers call this variety of the stone "precious topaz". The best-known precious topaz gems range in color from rich yellow to light brown or pinkish red. Topaz is one of the hardest gem minerals. In the mineral table of hardness, it has a rating of 8, which means that a knife cannot cut it, and that topaz will scratch quartz.
The golden variety of precious topaz is quite uncommon. Most of the world's topaz is white or blue. The white and blue crystals of topaz are large, often weighing thousands of carats. For this reason, the value of topaz does not depend so much on its size as it does with diamonds and many other precious stones, where the value increases about four times with each doubling of weight. The value of a topaz is largely determined by its quality. But color is also important: blue topaz, for instance, is often irradiated to deepen and improve its color.
Blue topaz is often sold as aquamarine and a variety of brown quartz is widely sold as topaz. The quartz is much less brilliant and more plentiful than true topaz. Most of it is variety of amethyst: that heat has turned brown.
[ NOTE] : topaz / 'tэupжz; `topжz/ n (a) [U] transparent yellow mineral 黄玉(矿 物). (b) [C] semi-precious gem cut from this 黄玉; 黄宝石.

重点单词   查看全部解释    
uncommon [ʌn'kɔmən]

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adj. 不寻常的,不凡的,罕有的

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hardness ['hɑ:dnis]

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n. 坚硬,困难,严厉

 
determined [di'tə:mind]

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adj. 坚毅的,下定决心的

 
precious ['preʃəs]

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adj. 宝贵的,珍贵的,矫揉造作的
adv.

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valuable ['væljuəbl]

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adj. 贵重的,有价值的
n. (pl.)贵

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variety [və'raiəti]

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n. 多样,种类,杂耍

 
deepen ['di:pən]

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vt. 使 ... 加深,使 ... 强烈 vi. 加深

 
compound ['kɔmpaund]

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n. 混合物,复合词
n. 院子(用围墙圈起来

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range [reindʒ]

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n. 范围,行列,射程,山脉,一系列
v. 排

 
quality ['kwɔliti]

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n. 品质,特质,才能
adj. 高品质的

 

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