A. The stars indicate that it is a oxidation state specific analysis, so you only use these if you have Fe3+ and Fe2+ analyses directly from the laboratory. Fe3+ data should be aliased to Fe2O3* and Fe2+ data should be aliased to FeO*. The specific oxidation state of iron is used in certain classification diagrams and calculations and both Fe2O3* and FeO* must be aliased otherwise the diagram or calculation will be greyed out.
Fe, FeO and Fe2O3 are treated as total iron. FeO is total iron expressed as ferrous oxide and Fe2O3 is total iron expressed as ferric oxide.
See Calculation>Provided menu to convert Fe data to total or explicit Fe states if they are not already available in the dataset.