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GRE阅读题目解析:无法鉴定钻石形成的年代

2016-12-14 17:12:00来源:网络

  【GRE阅读题目解析:无法鉴定钻石形成的年代GRE考试考什么?GRE阅读是重点。新东方在线GRE频道为大家带来GRE阅读题目解析:无法鉴定钻石形成的年代答案见下一页,希望对大家GRE备考有所帮助。更多精彩尽请关注新东方在线GRE频道!

  查看全部:GRE阅读答案解析(汇总)

  GRE阅读题目解析:无法鉴定钻石形成的年代

  P1

  Diamonds, an occasional component of rare igneous rocks called lamproites and kimberlites, have never been dated satisfactorily.

  However, some diamonds contain minute inclusions of silicate minerals, commonly olivine, pyroxene, and garnet.

  These minerals can be dated by radioactive decay techniques because of the very small quantities of radioactive trace elements they, in turn, contain.

  Usually, it is possible to conclude that the inclusions are older than their diamond hosts, but with little indication of the time interval involved.

  Sometimes, however, the crystal form of the silicate inclusions is observed to resemble more closely the internal structure of diamond than that of other silicate minerals.

  When present, the resemblance is regarded as compelling evidence that the diamonds and inclusions are truly cogenetic. (121 words)

  1. The author implies that silicate inclusions were most often formed

  (A) with small diamonds inside of them

  (B) with trace elements derived from their host minerals

  (C) by the radioactive decay of rare igneous rocks

  (D) at an earlier period than were their host minerals

  (E) from the crystallization of rare igneous material

  2. Select the sentence in the passage that indicates a way to determine the age of silicate minerals included in diamonds.

  点击下一页查看答案:

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