Diamonds are almost impossible to detect directly because they are so

Timer : 10min 43sec

1) The primary purpose of the passage is to
A. discuss an objection to Gurney’s theories about the uses of indicator minerals
Incorrect, as Gurney's theories are discussed only in the last 10-15 lines of the Paragraph.

B. explore the formation of diamonds and the reasons for their scarcity
Incorrect, no details regarding formation of diamonds is given.

C. analyze the importance of kimberlite pipes in the formation of diamonds
Incorrect, the passage describes relation between the kimberlite pipes and the diamond. It does state the importance anywhere.

D. define the characteristics of indicator minerals under differing conditions
Incorrect, Indicator minerals surface only in the second half of the passage. Also the characteristics of Indicator mineral are not discussed in "Differing Conditions"

E. explain a method of determining whether kimberlite pipes are likely to contain diamonds
Correct, the passage starts with the discussion of Kimberlite pipe, their formation, their characteristics and their relation with "Indicator Minerals".

2) 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 - Correct, used to describe properties of ilmenites
B. commonness of occurrence - Incorrect, a type of garnet typically found in diamond-rich pipes
C. chemical signature - Incorrect, are lower in calcium and higher in chrome than garnets from barren pipes.
D. place of formation - Incorrect, Geochemists John Gurney showed that garnets with this composition were formed only in the diamond-stability field
E. appearance in conjunction with diamonds - Incorrect, a type of garnet typically found in diamond-rich pipes

3) 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- Incorrect, 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.No reference of G10 w.r.t. 90%.

B. the levels of calcium and chrome in the pipe are conducive to diamond formation - Incorrect, are lower in calcium and higher in chrome than garnets from barren pipes. Passage and Choice B mean different.

C. the pipe passed through a diamond-stability field and thus may contain diamonds. Correct, Geochemists John Gurney showed that garnets with this composition were formed only in the diamond-stability field;

D. any diamonds the pipe contains would not have come from the diamond-stability field. Incorrect

E. the pipe’s temperature was so high that it oxidized any diamonds the pipe might have contained. Incorrect, the oxidation is referred to Ilemnite and not Garnet.


4) 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. Correct, When iron became highly oxidized, so did diamonds; that is, they vaporized into carbon dioxide.
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.

Goodluck
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