- UID
- 929697
- 在线时间
- 小时
- 注册时间
- 2013-8-28
- 最后登录
- 1970-1-1
- 主题
- 帖子
- 性别
- 保密
|
Diamonds are almost impossible to detect directly because they are so rare: very rich kimberlitepipes, the routes through which diamonds rise, may contain only three carats of diamonds per ton of kimberlite. Kimberlite begins as magma in Earth's mantle (the layer between the crust and the core). As the magma smashes through layers of rock, it rips out debris, creating a mix of liquid and solid material. Some of the solid material it brings up may come from a so-called diamond-stability field, where conditions of pressure and temperature are conducive to the formation of diamonds. If diamonds are to survive, though, they must shoot toward Earth's surface quickly. Otherwise, they revert to graphite or burn. Explorers seeking diamonds look for specks of "indicator minerals" peculiar to the mantle but carried up in greater quantities than diamonds and eroded out of kimberlite pipes into the surrounding land. The standard ones are garnets, chromites, and ilmenites. One can spend years searching for indicators and tracing them back to the pipes that are their source; however, 90 percent of kimberlite pipes found this way are barren of diamonds, and the rest are usually too sparse to mine.
In the 1970's the process of locating profitable pipes was refined by focusing on the subtle differences between the chemical signatures of indicator minerals found in diamond-rich pipes as opposed to those found in barren pipes. For example, G10 garnets, a type of garnet typically found in diamond-rich pipes, are lower in calcium and higher in chrome than garnets from barren pipes. Geochemists John Gurney showed that garnets with this composition were formed only in the diamond-stability field; more commonly found versions came from elsewhere in the mantle. Gurney also found that though ilmenites did not form in the diamond-stability field, there was a link useful for prospectors: when the iron in ilmenite was highly oxidized, its source pipe rarely contained any diamonds. He rea- soned that iron took on more or less oxygen in response to conditions in the kimberlitic magma itself—mainly in response to heat and the available oxygen. When iron became highly oxidized, so did diamonds; that is, they vaporized汽化,蒸发 into carbon dioxide.
这篇文章读得有点恶心,好几个专有名词,虽然尝试着用首字母代替还是读得糊里糊涂。文章基本读懂,细节把握不行。第一段没问题,第二段被绕晕。
P1:讲了一下diamond怎么形成,先说了一个找钻石的方法,不过貌似效果不太好---last sentence。
P2:1970的时候这个process被改变了,focus on不同钻石含量的化学物质差别上,举了个例子。出来一个科学家,具体解释这个改变,又提出一个I的例子(就是这个例子没搞明白到底放在这是干嘛的)---从反面说即使不在 diamond-stability field,也可以通过化学信号来帮助勘探者---相当于是进一步解释。
Q:Each of the following is mentioned in the passage as a difference between G10 garnet and other versions of garnet EXCEPT
A level of oxidation
B commonness of occurrence
C chemical signature
D place of formation
E appearance in conjunction with diamonds
正确答案 A
你的答案B
A显然讲的是后面的事,定位不能跨层,原处定位就好了。其实是非常明显的并列。
The passage suggests that the presence of G10 garnet in a kimberlite pipe indicates that
A the pipe in which the garnet is found has a 90% chance of containing diamonds---第一段的,跨段
B the levels of calcium and chrome in the pipe are conducive使容易发生的 to diamond formation---几乎是原句的改写Geochemists John Gurney showed that garnets with this composition...
C the pipe passed through a diamond-stability field and thus may contain diamonds---无关
D any diamonds the pipe contains would not have come from the diamond-stability field---无关
E the pipe's temperature was so high that it oxidized any diamonds the pipe might have contained---再次跨层,后面说到氧化的事其实是个另一方面的例子
正确答案 B
你的答案E
|
|