新东方英语背诵美文50篇 第三十七篇 Topaz
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.
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新东方英语背诵美文50篇 | |
- 新东方英语背诵美文30篇 第一篇 Youth 青春
- 新东方英语背诵美文30篇 第二篇 Three Days to See(Excerpts) 假如给我三天光明
- 新东方英语背诵美文30篇 第三篇 Companionship of Books 以书为伴
- 新东方英语背诵美文30篇 第五篇 Ambition 抱负
- 新东方英语背诵美文30篇 第四篇 If I Rest, I Rust 如果我休息,我就会生锈
- 新东方英语背诵美文30篇 第六篇 What I have Lived for 我为何而生
- 新东方英语背诵美文30篇 第七篇 When Love Beckons You 爱的召唤
- 新东方英语背诵美文30篇 第八篇 The Road to Success 成功之道
- 新东方英语背诵美文30篇 第九篇 On Meeting the Celebrated 论见名人
- 新东方英语背诵美文30篇 第十篇 The 50-Percent Theory of Life 生活理论半对半