What is a Mole of Olivine

We derived this relationship for a gas species because it is possible to differentiate between the species N2 and the component N2. In crystalline solutions there are no species, but there certainly is a wide choice of components. Consider for example the forsterite-fayalite crystalline solution. Normally we write forsterite as Mg2Si04 and fayalite as Fc2Si04. Is this the best choice of components, or should we choose MgSio.s02 - FeSio.502, or Mg4Si208 - Fe4Si20s, or. ..  

From the discussion of the nitrogen case, we know that 

The question now is, what practical difference does this make Perhaps the easiest way to show this is to consider Raoult s Law, which for a crystalline solution (equation (11.29)) says that 

Now you have to realize that the mole fraction X is unaffected by the choice of component problem we have been considering, that is, 

The problem is more difficult in other systems. How does one choose components in a complex silicate melt, for example In a melt there are no stoichiometric 

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