How to convert wt% MgCO3 to mole% MgCO3

I have geochemistry data for limestone samples consists of oxides and REE. I want to find out the mole% MgCO3 for the samples. I understand that I can use conversion factor of 3.4683 to convert MgO wt% to MgCO3 wt%. But from there I don't know how to proceed. Do I need to convert all of my data to moles first and proceed to calculate the mole%. And if all do I need to convert both oxides and REE or just the oxides

Would be really grateful for the help

If Could you please post here the your entire question ,it would more sense to us then.