托福IBT必背經(jīng)典文章：黃寶石

托福IBT必背經(jīng)典文章：黃寶石

【新東方托福IBT必背50篇經(jīng)典文章：黃寶石】這份資料可以幫助考生在托福網(wǎng)考備考過程中，提高托?？谡Z水平，同時對提高托福寫作水平和托福閱讀都有很大幫助。托福IBT必背50篇經(jīng)典文章，助你托?？荚嚦晒?

新東方托福IBT必背50篇經(jīng)典文章：黃寶石

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 黃玉(礦物).

(b) [C] semi-precious gem cut from this 黃玉; 黃寶石.

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