GWD6-Q23 to Q26:

[agk99]

GWD6-Q23 to Q26: (鑽石題)

Diamonds are almost impos-
sible to detect directly because they
are so rare: very rich kimberlite
Line pipes, the routes through which
(5) diamonds rise, may contain only
three carats of diamonds per ton
of kimberlite. Kimberlite(講的是一種成色極佳的南非鑽石) begins as
magma in Earth’s mantle (the layer
between the crust and the core). As
(10) 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
(15) diamond-stability field, where condi-
tions of pressure and temperature
are conducive to the formation of
diamonds. If diamonds are to sur-
vive, though, they must shoot toward
(20) Earth’s surface quickly. Otherwise,
they revert to graphite or burn. 這裡是第一個重點，講的是說如果
沒有快速衝出地表，就會變成石墨或是燒掉了 Explorers seeking diamonds look
for specks of “indicator minerals”
peculiar to the mantle but carried up
(25) in greater quantities than diamonds
and eroded out of kimberlite pipes
into the surrounding land. The stan-
dard ones are garnets(石榴石), chromites(鉻鐵),
and ilmenites(鈦鐵). One can spend years
(30) 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
(35) are usually too sparse to mine. 這肯定是第二個重點，就是說透過一些方法來找，是可以勉強找到，但效果很差，不符成本原則 In the 1970’s the process of
locating profitable pipes was refined
by focusing on the subtle differ-
ences between the chemical
(40) 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
(45) diamond-rich pipes, are lower in
calcium and higher in chrome than
garnets from barren pipes. (這裡有題，請特別留意)Geo-
chemists John Gurney showed that
garnets with this composition were
(50) formed only in the diamond-stability
field; more commonly found ver-
sions came from elsewhere in the
mantle. Gurney also found that
though ilmenites did not form in the
(55) diamond-stability field, there was a
link useful for prospectors: when
the iron in ilmenites was highly
oxidized(生鏽), its source pipe rarely
contained any diamonds.這裡是指，garnet總是出現在有鑽石的地方，而ilmenites要是生鏽，就不會有鑽石，iron有氧存在，就不是鑽石生長的地方He rea-
(60) 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 avail-
able oxygen. When iron became
(65) highly oxidized, so did diamonds;
that is, they vaporized into carbon
dioxide. 就不是鑽石，而是蒸發為二氧化碳，注意最後一段的最後一句

[agk99]

Q23: Ｅ
The primary purpose of the passage is to

A. discuss an objection to Gurney’s theories about the uses of indicator minerals (錯在objection)
B. explore the formation of diamonds and the reasons for their scarcity (只有第二段)
C. analyze the importance of kimberlite pipes in the formation of diamonds (analyze必錯)
D. define the characteristics of indicator minerals under differing conditions (找不到define)
E. explain a method of determining whether kimberlite pipes are likely to contain diamonds
可以仔細看第一段與第二段的比較，這是傳統研究與新研究的敘述，但重點都是講如何找到鑽石，
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Q24: A
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 第51行
C. chemical signature 第40行
D. place of formation 第41至43行
E. appearance in conjunction with diamonds 第45行

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Q25: C
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
B. the levels of calcium and chrome in the pipe are conducive to diamond formation
C. the pipe passed through a diamond-stability field and thus may contain diamonds
D. any diamonds the pipe contains would not have come from the diamond-stability field
E. the pipe’s temperature was so high that it oxidized any diamonds the pipe might have contained
A必錯，B是錯在後半段，有conducive效果的是溫度與壓力(見第十七行)。D錯在not，E無關
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Q26: C
According to the passage, Gurney refined the use of ilmenites in prospecting for diamonds in which of the following ways?

A. He found that ilmenites are brought up from the mantle by kimberlite pipes and erode out into the surrounding land in greater quantities than diamonds.
B. He found that since ilmenites do not form in the diamond-stability field, their presence indicates the absence of diamonds.
C. He showed that highly oxidized iron content in ilmenites indicates a low survival rate for diamonds.
D. He found that when the iron in ilmenites is highly oxidized, conditions in the magma were probably conducive to the formation of diamonds.
E. He showed that ilmenites take on more or less oxygen in the kimberlite pipe depending on the concentration of diamonds.
C的選項就在56行畫線部分，B則是錯在absence，不是沒有，而是看生鏽的程度而決定鑽石的多寡

[gogotu]

我提供一點在http://pilot.mse.nthu.edu.tw/87%BA%F4%AD%B6%C4v%C1%C9/HOMEPAGE/%C0s%ACf%B5%D8/form.htm 找到的背景：
天然鑽石原產於超過兩百公里深度的地下。它的形成年代通常為24至32億年前之間，但也有短至6千萬年者。這種地底深處的鑽石有時會隨深處熔岩的上昇而帶至地表。這種深層熔岩凝固 時形成上大下小喇叭狀的岩柱。這種含鑽石的岩柱的礦物成分很特別(如只有高壓下才生成的石榴子石)稱為"Kimberlite"。 Kimberlite只生成於古老穩定的地殼中，全世界只有在特定的區域內才能看到這種深層岩柱的露頭。(如印度、巴西、南非、薩伊、俄羅斯、中國及澳洲)。
Kimberlite的露頭風化後鑽石會被雨水沖刷而沈積在河床內。山洪爆發後這些鑽石也會被河水沖到河口而混在岸邊沙灘內，最早被發現的鑽石就是這類漂積的鑽石。經由河床沈積鑽石的指引，鑽石的母床，Kimberlite才漸被發現。現在鑽石的來源差不多都是從Kimberlite中採出。但Kimberlite內所含的鑽石量也很稀少，通常要壓碎五公噸以上的鑽石才能找到一克拉(1/5克)的鑽石。而且大部分鑽石的品質不 佳:只能成為工業用磨料。能用做寶石的鑽石不及鑽石原石的1/7。

[stilalala]

關於25題

我發現cd上有人在爭論答案是b or c

我個人傾向b
但也有人認為b是過度推論

認為c用may是比較合理的

不知道各位大大怎麼想??

謝謝

我想我知道答案了

應該是c

剛剛又把agk大大的解釋看過一次

我懂了

不好意思^^

[oguz]

請教一下24題
E選項哪裡有提到呢?
agk99大大的解釋說在Line45
但我覺得那比較傾向於講garnet的"成分"
與 appearance有什麼關聯呢?

另，25題 A錯在哪裡呢?
Line44-45不是提到
G10 garnets, a type of garnet typically found in diamond-rich pipes, are....

謝謝

[James0713]

再推一下oguz的問題　

[ivy]

回oguz的25題A
雖然文章說在diamond-stability field找到的may contain diamonds
但沒有說會有90%的機率contain diamonds
所以應該還是C對
希望有回答到你的問題!!

[nexxt0722]

Q24: A
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 第51行
C. chemical signature 第40行 -->第45,46行
D. place of formation 第41至43行 -->第50行
E. appearance in conjunction with diamonds 第45行 -->第44,45行,found in diamond-rich pipes

[coruscant]

同意 第24題選項E 實在是找不到文章中哪裡有提到appearance...

[medi66]

nexxt0722的回文 就有提到啦
G10都會出現在diamond-rich pipes
而其他的garnet都是出現在barren pipes
這就是他們不一樣的地方

所以Q24答案還是A才對唷

[doki28]

Q24 答案選項e中的appearance在這裡指的是”出現”而非”外觀”
會選e應該是誤會appearance的意思吧....

[A級垂耳兔]

24題答案a與G10等garnet無關...文中提到氧化程度是指ilm~那種鐵氧化程度高...代表熱和氧高...鑽石就有可能被燒掉...
文中最後一段題到兩種判定方式...一種就是G10..另一種就是ilm~那種鐵氧化程度...