internal standard for glass

[Ferdinando Costantino]

Dear all I'm doing quantitative analysis on a mixture of  6 or 7 phases and I must to know the weight fraction of amorphous phases. I'm using Si as internal standard but I'didn't understand if I must consider the relative or absolute difference between the real and calculeted quantity. For example: if I put in the mixture 5% of Si and GSAS read 7% the relative error is 40%, Is this the quantity that I must subtract from each phase and sum to obtain the amorphous, or the process is different? thanks in advance.                                                              Ferdinando Costantino                                                              dipartimento di Scienze della terra                                                              Università di Perugia.