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Biswajit Swain posted an Question
January 30, 2021 • 00:53 am 30 points
  • IIT JAM
  • Geology (GG)

Q30. the change in coordination number of silicon (s1) when a-quartz transforms to stishovite, which has octahedral coordination, is (a) 2 (c) 6 (b) 4 (d) 8

Q30. The change in coordination number of silicon (S1) when a-quartz transforms to stishovite, which has octahedral coordination, is (A) 2 (C) 6 (B) 4 (D) 8

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    Sajan sarthak best-answer

    The coordination number of stishovite is 6, so the silicon atoms are all surrounded by 6 oxygen atoms. The crystal structure of stishovite does not fit in the classification scheme of silicates, so stishovite could well be considered a non-silicate. Stishovite and coesite are both not stable at normal pressures and normal temperatures, but since their transitions into a low pressure silica polymorphs are reconstructive phase transitions that involve a complete rearrangement of the atoms in the crystal lattice, both are metastable at normal conditions. Coordination no of Alpha quartz is 4 so Difference is 6-4 = 2

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    Saurabh 1 best-answer

    Coordination number of stishovite(high pressure polymorph of quartz having highest density in the quartz family Or polymorphs) is 6 , generally it doesn't have the characteristic tectosilicate structure, while the coordination number of alpha quartz(Or other polymorph of quartz) is 4. So difference is 6-4 = 2 . Correct option is A.

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