新东方背诵文选 L38 Topaz
时间：2005-05-03 16:00:00
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（单词翻译）
Topaz is a hard,
transparent1 mineral. It is a compound of
aluminum2, silica, and fluorine.
Gem3 topaz is valuable. Jewelers call this variety of the stone "precious topaz". The best-known precious topaz
gems4 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
quartz5.
The golden variety of precious topaz is quite
uncommon6. 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
determined7 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
plentiful8 than true topaz. Most of it is variety of
amethyst9: 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.
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