STOICHIOMETRY
A fixed atomic ratio between elements. For example the mineral olivine has a stoichiometry of (Fe,Mg):Si:O of 2:1:4 (atomic). A test for a "good" analysis would be to calculate (Analyze!|Calculation Options) the stoichiometry on the basis of 4 oxygens. Values for Si of .997 and sum for Fe and Mg of 1.995 would be generally considered very good.