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 worlds 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.
2016届高三英语二轮复习作业卷:32(含解析)(河北衡水)
2016届高三英语二轮复习作业卷:22(含解析)(河北衡水)
2016届高考英语二轮词法专题讲座素材:10 情态动词
2016年高考英语二轮复习课件:必修4 Unit 3 A taste of English humour(新人教版)
2016届高三英语二轮复习作业卷:1(含解析)(河北衡水)
2016届高三英语二轮复习作业卷:38(含解析)(河北衡水)
2016年高考英语二轮复习课件:选修7 Unit 3 Under the sea(新人教版)
2016年高考英语二轮复习课件:选修8 Unit 3 Inventors and inventions(新人教版)
2016届高三英语二轮复习作业卷:29(含解析)(河北衡水)
2016年高考英语二轮复习课件:选修8 Unit 4 Pygmalion(新人教版)
2016年高考英语二轮复习课件:选修7 Unit 4 Sharing(新人教版)
2016届高考英语二轮词法专题讲座素材:15 反意疑问句
2016年高考英语二轮复习课件:必修4 Unit 1 Women of achievement(新人教版)
2016届高三英语二轮复习作业卷:21(含解析)(河北衡水)
2016届高三英语二轮复习作业卷:9(含解析)(河北衡水)
2016届高三英语二轮复习作业卷:34(含解析)(河北衡水)
2016届高三英语二轮复习作业卷:11(含解析)(河北衡水)
2016届高三英语二轮复习作业卷:39(含解析)(河北衡水)
白宫为计划废除奥巴马时期互联网隐私规定辩护
2016届高考英语二轮词法专题讲座素材:12 主谓一致
2016届高三英语二轮复习作业卷:6(含解析)(河北衡水)
2016届高三英语二轮复习作业卷:18(含解析)(河北衡水)
2016年高考英语二轮复习课件:必修4 Unit 2 Working the land(新人教版)
2016届高三英语二轮复习作业卷:12(含解析)(河北衡水)
2016年高考英语二轮复习课件:必修5 Unit 1 Great scientists(新人教版)
2016年高考英语二轮复习课件:选修8 Unit 5 Meeting your ancestors(新人教版)
2016届高三英语二轮复习作业卷:8(含解析)(河北衡水)
2016届高三英语二轮复习作业卷:30(含解析)(河北衡水)
2016届高考英语二轮词法专题讲座素材:14 感叹句
2016届高考英语二轮词法专题讲座素材:13 倒装句
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |