InterviewSolution
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InterviewSolution
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The `"OLIVINE"` series of minerals consists of crystal in which `Fe^(2+)` and `Mg^(2+)` ions may substitute for each other causing susbstitutional impurity defects without changing the volume of unit cell. In `"OLIVINE"` series of minerals, `O^(2-)` ions exist as fcc with `Si^(4+)` occupying one-fourth of `OVs` and divalent metal ions occupying one-fourth of `OVs` and divalent metal ions occupying one-fourth of `TVs`. The density of "forsterite" (magnesium silicate) is `3.21 g cm^(-3)` land that of "fayalite" (ferrous silicate) is `4.34 g cm^(-3)`. The formula of "fayalite mineral" isA. `Fe_(2)SiO_(4)`B. `FeSiO_(4)`C. `Fe_(2)SiO_(6)`D. `Fe_SiO_(3)` |
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Answer» Correct Answer - A For fcc, Number of `O^(2-)` ion=`8 ("corner") xx (1)/(8) "per corner share"` ltbr. `+ 6 ("faces") xx (1)/(2) "per face share"` `= 4` Number of `Si^(4+)` ions `= 1/4 xx "OV" = 1/4 xx 4 = 1//"unit cell"` Number of `Fe^(2+)` ions `= 1/4 xx "TV" = 1/4 xx 8 = 2//"unit cell"` So, formula of `"FAYLITE"` is `overset(+2xx2)(Fe_(2))Si^(4+)O_(4^(2-))` `rArr Fe_(2)SiO_(4)` |
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