Provide answers and discussions for the following questions and points: What ele

Question

Provide answers and discussions for the following questions and points: What element(s) would you expect to substitute for Mg in olivine? Why did you choose these? What is (are) the name(s) for the different chemical end members of olivine? Magnetite and spinal are each members of the 'spinal group.' What elemental substitutions would you expect to form other minerals in the spinal group? List the chemical formulas and describe the substitution mechanism for each spinal you define: How many complete atoms and fractions of atoms are represented for oxygen and silicon in the unit cell of alpha-quartz? Is your total for oxygen and silicon consistent with the formula for quartz? state the 'chemical formula' for the anion complex in quartz. Is this inconsistent with an overall chemical formula of SiO2 for quartz? Describe anions are shared to arrive at the formula of SiO2 in quartz:

Explanation / Answer

1) olivine is (Mg+2, Fe+2)2SiO4

we will preffer bivalent ions has similar ionic radie as Mg2+ best option is Fe2+

fayalite and forsterite.

forsterite is Mg rich compound (Mg2SiO4)

Fayalite is the iron rich member with a pure formula of Fe2SiO4.

2)

magnetite = chemical formula Fe3O4 is inverse spinnel

Fe2+ (Fe3+)2 O4 here one part is F2+ other is Fe3+ But distribution of Fe in void is differ from spinnel structure

half Td void filled by Fe3+ and Oh void filled by rest Fe3+ . Fe2+ is filled only in remaining Td void

Spinel = AB2O4 A = +2 B = +3 . Here +3 oxidation state B will occupy only in Oh void . +2 oxidation state A occupy only in Td void e.g Mn3O4

Fe3O4 + Ca -> CaFe2O4 ................... (Ca)2+ 2(Fe3+) O4

Mn3O4 + Ca -> CaMn2O4 ................. (Ca)2+ 2(Mn3+) O4

3)

SiO2 has structure similar to diamond.Quartz has a very complicated crystal structure, which involves interwoven helical chains. All silicates involve silicon in tetrahedral environments surrounded by oxygen atoms.each silicon atom is bridged to its neighbours by an oxygen atom.In quartz there are 3 Si and 6 O atoms in the unit cell, Si3O6.

4)excample for anion complex of silicate MgSiO4-FeSiO4 so [SiO4]2- does not consistant with over all chemical formulae of SiO2. crystal structure incorporates aspects of the orthorhombic P Bravais lattice, which arise from each silica (SiO4) unit being joined by metal divalent cations with each oxygen in SiO4 bound to 3 metal ions. It has a spinel-like structure similar to magnetite but uses one quadravalent and two divalent cations M2+2 M+4O4 instead of two trivalent and one divalent cations.

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